US 5,307,631 AGranted

Hydraulic control apparatus for hydraulic construction machine

AssigneeHitachi Construction Machinery Co., Ltd.

InventorsAkira Tatsumi, Seiji Tamura, Mitsuo Kihara, Kazuhiro Ichimura, Hiroshi Onoue, Shigetaka Nakamura

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Abstract

The displacement of a variable displacement hydraulic pump (1) which is driven by a diesel engine (27) is so controlled as to be set to a first target displacement to keep a pump pressure higher than a load pressure by a predetermined target value, or a second target displacement to limit an input torque on the basis of the pump pressure. Provided is a stand-by flow rate control portion (65) which outputs a third target displacement larger than the minimum value of said first target displacement. The displacement of the pump (1) is controlled so as to be set to the third target displacement when the third target displacement is output from the stand-by flow rate control portion (65).

Claims25

Dependent claims

A hydraulic control apparatus for a hydraulic construction machine including:

a variable displacement hydraulic pump which is driven by a prime mover;
a first hydraulic actuator which is driven by delivery oil from said hydraulic pump;
a first control valve which is provided between said hydraulic pump and said first hydraulic actuator and serves to control pressured oil to be supplied to said first hydraulic actuator;
first determination means for determining a first target displacement to keep a delivery pressure of said hydraulic pump to a value higher than a load pressure of the first hydraulic actuator by a predetermined target value;
second determination means for determining a second target displacement by which an input torque is limited on the basis of said delivery pressure of said hydraulic pump;
and
displacement control means for controlling said displacement of said hydraulic pump such that said displacement is equal to at least one of said first and second target displacements,
said hydraulic control apparatus further including instructing means for issuing instructions that an oil flow rate of said variable displacement hydraulic pump becomes a predetermined minimum value, and limiting means for imposing limitation in response to said instructions on a signal indicating said first target displacement which is determined and output by said first determination means, so that the minimum oil flow rate becomes larger than that before limitation is imposed at least when said hydraulic pump is driven with a light load.

5 more elements

In a hydraulic control apparatus for a hydraulic construction machine including;

first operating means which is manipulated to keep the rotational speed of a prime mover to an arbitrary rotational speed,
second operating means which is manipulated to control the rotational speed of said prime mover and is returned to an initial position of low rotational speed when the manipulating force is released,
rotational speed control means for controlling the rotational speed of said prime mover in accordance with said first and second operating means,
a variable displacement hydraulic pump which is driven by said prime mover,
a first hydraulic actuator which is driven by a delivery oil from said hydraulic pump,
a second hydraulic actuator which is driven by said delivery oil of said hydraulic pump,
a first control valve which is provided between said hydraulic pump and said first hydraulic actuator and serves to control a pressured oil supplied to said first hydraulic actuator,
a second control valve which is provided between said hydraulic pump and said second hydraulic actuator and serves to control a pressured oil supplied to said second hydraulic actuator,
first determination means for determining a first target displacement to keep said delivery pressure of said hydraulic pump to a value higher than load pressure of said first and second hydraulic actuators by a predetermined target value,
second determination means for determining a second target displacement by which an input torque is limited on the basis of said delivery pressure of said hydraulic pump, and,
displacement control means for controlling said displacement of said hydraulic pump so that said displacement is equal to at least one of said first and second target displacements,
said control apparatus further including;
judging means for outputting a discrimination signal on the basis of a discrimination of a state where said first hydraulic actuator is operated while the rotational speed of said prime mover is controlled by said second operating means, wherein,
when said discrimination signal is output, said displacement of said variable displacement hydraulic pump is so controlled that it is equal to said second target displacement irrespective of the value of said first target displacement.

11 more elements

In a hydraulic control apparatus for a hydraulic construction machine including;

a first manual operation member which is manipulated to adjust a diesel engine so as to have an arbitrary rotational speed,
a travelling pedal which is manipulated to control the travelling speed of a vehicle and is returned to its initial position when the manipulating force is released,
rotational speed control means for controlling the rotational speed of said diesel engine in accordance with the operation amount of said manual operation member and said travelling pedal,
a variable displacement hydraulic pump which is driven by said diesel engine, a hydraulic actuator for a front attachment which is driven by a delivery oil from said hydraulic pump,
a hydraulic motor for a vehicle travelling which is driven by said delivery oil of said hydraulic pump,
a control valve for said front attachment which is provided between said hydraulic pump and said hydraulic actuator for said front attachment and serves to control a pressured oil supplied to said hydraulic actuator,
a control valve for a vehicle travelling which is provided between said hydraulic pump and said hydraulic motor for the vehicle travelling and serves to control a pressured oil supplied to said hydraulic motor for the vehicle travelling in accordance with the step-on amount of said travelling pedal,
first determination means for determining a first target displacement to keep said delivery pressure of said hydraulic pump to a value higher than load pressure of said hydraulic actuators for said front attachment and the travelling by a predetermined target value,
second determination means for determining a second target displacement to limit an input torque on the basis of said delivery pressure of said hydraulic pump, and,
displacement control means for controlling said displacement of said hydraulic pump so that said displacement is equal to one of said first and second target displacements,
said control apparatus further including;
judging means for outputting a discrimination signal on the basis of a discrimination of a state where said hydraulic actuator for said front attachment is operated while the rotational speed of said diesel engine is controlled by said travelling pedal, and,
selecting means for selecting said second target displacement irrespective of said first target displacement when said discrimination signal is output.

10 more elements

Dependencies are inferred from the claim text.