US 5,447,027 AGranted

Hydraulic drive system for hydraulic working machines

AssigneeHitachi Construction Machinery Co., Ltd.

InventorsKoji Ishikawa, Toichi Hirata, Genroku Sugiyama

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Abstract

A hydraulic drive system comprises a controller (12) and several condition sensors. A boom-up target flow rate setting section determines a boom-up target flow rate based on signals from a pressure sensor (11) and a rotational speed meter (16), a pump delivery rate detecting section determines a pump delivery rate based on signals from a tilt angle sensor (15) and the rotational speed meter (16), a differential pressure detecting section and a center bypass flow rate calculating section determine a center bypass flow rate based on signals from pressure sensors (9, 10), a boom cylinder calculating section determines a boom cylinder flow rate from the pump delivery rate and the center bypass flow rate, and a first pump target displacement volume calculating section calculates a first pump target tilt angle .theta..sub.1 in accordance with the difference between the boom-up target flow rate and the boom cylinder flow rate. In this case, .theta..sub.1 is larger than a second pump target tilt angle .theta..sub.2 for negative control and is selected by a maximum value selecting section. Then, a minimum value selecting section selects the smaller one of .theta..sub.1 and a maximum tilt angle .theta..sub.max determined with horsepower control, and drive signal generating section outputs a corresponding target current to a solenoid proportional valve (13) for driving a piston (6a) of a regulator (6) to the right in FIG. 4.

Claims12

Dependent claims

A hydraulic drive system for hydraulic working machines comprising a variable displacement hydraulic pump (2), a first actuator (3) driven by a hydraulic fluid delivered from said hydraulic pump (2), a first directional control valve (1) of center bypass type having meter-in passages (b.sub.1, b.sub.2) provided with meter-in variable restrictors (55a, 55b) and a center bypass passage (1a) provided with bleed-off variable restrictors (54a, 54b) for controlling a flow of the hydraulic fluid supplied from said hydraulic pump (2) to said first actuator (3), first operation means (8;

75, 75a, 75b, 12, 72, 73;
53a, 53b) for controlling a stroke amount of said first directional control valve (1), a low pressure circuit (45), a center bypass line (51) for connecting said center bypass passage (1a) to said low pressure circuit (45) at a point downstream of said bleed-off variable restrictors (54a, 54b), and a regulator (6) for controlling a displacement volume of said hydraulic pump (2), wherein:
said hydraulic drive system further comprises first operation amount detecting means (11;
75a, 75b) for detecting a operation amount of said first operation means (8;
75, 75a, 75b, 12, 72, 73;
53a, 53b);
first target flow rate setting means (12) for setting a first target flow rate of said first actuator (3) in accordance with said operation amount detected;
flow rate determinate means (15, 16;
4, 9, 10, 5a, 5b;
12) for determining an actual actuator flow rate supplied to said first actuator (3);
and
regulator control means (12, 13) for controlling the drive of said regulator (6) so that said actual actuator flow rate comes closer to said first target flow rate.

9 more elements

Dependencies are inferred from the claim text.