Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1997-11-14
1999-09-07
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60426, 60427, 60429, 91517, F16D 3102
Patent
active
059469102
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic circuit for a hydraulically driven working vehicle, and more particularly, to a hydraulic circuit for a hydraulically driven vehicle, which travels via drive wheels which are driven by a hydraulic motor which is driven by hydraulic pumps which are driven by an engine, and which has a working machine attached thereto.
BACKGROUND ART
Hydraulically driven working vehicles have been known in which a hydraulic travel pump and a working machine hydraulic pump are driven by an engine, a travel motor is rotated by pressurized oil, discharged from the hydraulic travel pump to drive a drive wheel for traveling, and a working machine cylinder is extended and contracted by pressurized oil, discharged from the working machine hydraulic pump, to actuate a working machine. As a hydraulic circuit for the above-described hydraulically driven working vehicles, a hydraulic circuit disclosed in, for example, Japanese Unexamined Patent Publication No. 57-208349 has been known. In the hydraulic circuit, a hydraulic travel pump and a hydraulic travel motor are subjected to a closed-circuit connection by first and second main circuits, and the capacity of the hydraulic travel pump (hereinafter, the capacity shows a discharge amount per one rotation, cc/rev) is changed to determine a traveling speed. At this time, pressurized oil, discharged from the working machine hydraulic pump, is supplied to a working machine cylinder by a working machine valve, and when the working machine valve is placed in its neutral position, the discharged oil is supplied to one of the first and the second main circuits. In this hydraulic circuit, the pressurized oil, discharged from the working machine hydraulic pump, is supplied to the hydraulic travel motor, and the hydraulic travel motor rotates at a speed which is higher than the rotational speed corresponding to a maximum discharge amount of the hydraulic travel pump, thereby traveling the vehicle at a high speed.
However, this hydraulic circuit requires a first directional control valve, for supplying the discharged oil to one of the first and second main circuits; a manually-operated second directional control valve; and a third directional control valve, which is placed in a drain position when pressurized oil to be supplied increases to a set pressure or higher. In addition, this hydraulic circuit requires a complicated mechanism for switching the first directional control valve, by transmitting a movement of an operation member for changing the discharge direction of the hydraulic travel pump to the control valve, and a mechanism for switching the second directional control valve; whereby the structure of the circuit becomes very complicated. Incidentally, the third directional control valve prevents the pressurized oil, discharged from the working machine hydraulic pump, from being supplied to the first and second main circuits when the pressure of the first main circuit or the second main circuit is the set pressure or higher, i.e., when a traveling resistance is high and the hydraulic travel motor rotates at a low speed. In addition, in this hydraulic circuit, if the working valve is changed from its neutral position to an operating position when the traveling resistance is low and the hydraulic travel motor is rotating at a high speed, the working machine hydraulic pump actuates the working machine, so that the hydraulic travel motor is not supported by the working machine hydraulic pump, and a constant traveling speed cannot be obtained. For this reason, it is dangerous for an operator to actuate the working machine while traveling, because the speed suddenly changes.
In addition, for example, when earth and sand are loaded on a bucket by a loader, and the loader approaches a dump truck at a slow speed, a problem arises in that the rotational speed of the hydraulic travel motor increases because the motor is supported by the working machine hydraulic pump, so that it becomes difficult for the operator to control the loader
REFERENCES:
patent: 3800669 (1974-04-01), Distler
patent: 3916625 (1975-11-01), Holtkamp
patent: 5211014 (1993-05-01), Kropp
patent: 5692377 (1997-12-01), Moriya et al.
Hayashi Seita
Nunotani Sadao
Komatsu Ltd.
Nguyen Hoang
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