Motors: expansible chamber type – With motive fluid valve – Relatively movable serial valves
Patent
1997-02-04
1998-09-29
Nguyen, Hoang
Motors: expansible chamber type
With motive fluid valve
Relatively movable serial valves
91448, 91451, 1375962, F15B 1108
Patent
active
058133100
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a working machine fall preventive valve apparatus. More particularly, the present invention relates to an apparatus which prevents the fall of any component of the working machine when a failure occurs in a hydraulic circuit for delivering a pressure fluid to a hydraulic cylinder for the operation of that working machine component. The working machine may be a construction machine such as a hydraulic excavating machine.
BACKGROUND ART
In general, a known hydraulic excavating machine has a construction in which a vehicle body has a boom mounted thereon by a boom cylinder so that the boom may be swung up and down. The boom, in turn, has an arm mounted thereto by an arm cylinder so that the arm may be swung up and down. In addition, the arm has a bucket swingingly secured thereto.
A hydraulic circuit delivers a pressure discharge fluid from a hydraulic pump to the respective cylinders in such a hydraulic excavating machine. The hydraulic circuit is provided in the discharge paths of the hydraulic pump with directional control valves for the boom, the arm and the bucket. Each directional control valve is switchingly operable to provide fluid communication between the respective control passages for controlling the fluid pressures corresponding to the boom cylinder, the arm cylinder and the bucket cylinder. The pump discharge paths on the other hand may selectively be established and blocked, thereby controlling an extending and a contracting operation of each such cylinder to control the behavior of each of the boom, the arm and the bucket.
With such a hydraulic circuit, each such cylinder is formed therein with a retention pressure producing chamber in which a retention pressure is developed in accordance with an external load such as the weight of the boom, the arm or the bucket. Such a retention pressure producing chamber is in fluid communication with a corresponding directional control valve via a fluid passage. Thus, when the corresponding directional control valve is set at a closed position, the chamber may act to maintain the fluid pressure between the chamber and the directional control valve and hence keep the corresponding boom, arm or bucket at a predetermined position. If the fluid passage connecting a given directional control valve and the corresponding retention pressure producing chamber is damaged while the boom, the arm or the bucket is held at a predetermined position, the pressure in the retention pressure producing chamber will decrease so that the cylinder may contact under an external load to cause the boom, the arm or the bucket supported thereby to immediately fall.
In order to prevent such a drop in the retention pressure within the retention pressure producing chamber under the operation of the hydraulic excavating machine, Japanese Unexamined Utility Model Publication No. Sho 5722554 has proposed an arrangement in which the fluid passage connecting a directional control valve and the retention pressure producing chamber of corresponding cylinder is provided with a working machine fall preventive valve apparatus. The apparatus, in turn, has a check valve, a flow rate control valve and a safety valve. In such an arrangement, when the fluid passage is damaged, the check valve will act to prevent a retention pressure from flowing out of the retention pressure producing chamber of the cylinder. Thus the boom will not fall due to the contraction of the cylinder under an external force.
The check valve is used to allow the operating fluid to flow from the directional control valve into the retention pressure producing chamber and to prevent the operating fluid from flowing out of the retention pressure producing chamber into the directional control valve. The flow rate control valve is held in a blocking state under a spring force. The flow rate control valve is brought to a communicating state in response to an external signal when the cylinder is contractively operated. Thus, the flow rate of the operating fluid from the retention pressure
REFERENCES:
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patent: 3929159 (1975-12-01), McAvoy
patent: 4716933 (1988-01-01), Stoever et al.
patent: 5062349 (1991-11-01), Khan
patent: 5372060 (1994-12-01), Maruyama et al.
patent: 5579676 (1996-12-01), Wilke
Hori Shuji
Karakama Tadao
Komatsu Ltd.
Nguyen Hoang
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