Motors: expansible chamber type – With motive fluid valve – Pilot valve
Reexamination Certificate
2002-07-16
2004-07-06
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
With motive fluid valve
Pilot valve
C060S422000
Reexamination Certificate
active
06758128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a technical field of an hydraulic circuit for a working machine, such as a hydraulic excavator, provided with various hydraulic actuators.
2. Description of Related Art
In general, various hydraulic actuators are provided in a working machine, such as a hydraulic excavator, and working machines exist, which have a structure such that, while control of pressure oil supply to these hydraulic actuators is performed by a pilot operated type control valve, supply of a pilot pressure to the control valve is performed by a pilot valve for outputting a pilot pressure based on an operation with an operating tool. As an example thereof, a hydraulic circuit of a hydraulic cylinder to be provided in a hydraulic excavator is shown in FIG.
6
. In
FIG. 6
,
1
denotes a hydraulic cylinder,
2
denotes a main hydraulic power source,
3
denotes a pilot hydraulic power source,
4
denotes a reservoir,
5
denotes a control valve, and
17
denotes a pilot valve (herein, in
FIG. 6
,
6
denotes a control valve for another hydraulic actuator
7
which shares an hydraulic power source of supply with the hydraulic cylinder
1
). In this hydraulic circuit, a pilot pressure to be outputted from the pilot valve
17
becomes higher as the degree of operation with a control lever
12
becomes greater and, in addition, as the pilot pressure to be supplied becomes higher, the degree of opening of the control valve
5
becomes greater, the amount of pressure oil to be supplied to the hydraulic cylinder
1
increases, and expanding/contracting speed of the cylinder
1
accelerates. That is, a structure is provided such that the cylinder expanding/contracting speed is controlled in a manner corresponding to the degree of operation with the control lever
12
, and the relationship between the degree of operation with the control lever
12
and cylinder expanding/contracting speed is as shown in
FIG. 7
, for example.
Meanwhile, in some cases where a minute operation is performed by slowly expanding/contracting the above hydraulic cylinder, such a maximum speed of the hydraulic cylinder as shown in
FIG. 7
is not required, but expanding/contracting actions of the cylinder within a low-speed range indicated as the fine operation area are desirable. However, the range of operation with the control lever is narrow within the above fine operation area, therefore, it is necessary to operate the control lever while suppressing the degree of operation to a small amount. This makes an operator nervous, requires a great deal of skill, and results in poor workability, in which problems to be solved by the invention exist.
SUMMARY OF THE INVENTION
In light of the circumstances described above, the invention is created with the aim of solving the problems and provides an oil hydraulic circuit comprising a pilot operated type control valve for performing control of pressure oil supply to a hydraulic actuator and a pilot valve gear for outputting a pilot pressure to the control valve, wherein the pilot valve gear comprises a first pressure control means for outputting a pilot pressure corresponding to the degree of operation with an operating tool and a second pressure control means for reducing the pilot pressure outputted from the first pressure control means based on an external signal and outputting the reduced pilot pressure to the control valve.
Then, by providing such a structure, the acting speed of the hydraulic actuator with respect to the degree of operation with the operating tool can be made slow. Thus, the operationality and workability are improved in, for example, a case where a fine operation is performed.
In the oil hydraulic circuit, the second pressure control means comprises pressure-reducing valves which can switch over the respective states to an inactive state for outputting the pilot pressure from the first pressure control means to the control valve without a reduction, and to an active state for outputting the pilot pressure after a reduction and selector valves which switch over to a first position and to a second position based on an external signal. Further, the selector valves act to bring, at the first position, the respective pressure-reducing valves into an inactive state and, at the second position, into an active state, whereby selection between the case where a pilot pressure to be outputted from the second pressure control means to the control valve is reduced and the case where the same is not reduced can be performed by a switchover of the selector valve based on an external signal.
REFERENCES:
patent: 5081905 (1992-01-01), Yagyu et al.
patent: 5102102 (1992-04-01), Hidaka et al.
patent: 5490384 (1996-02-01), Lunzman
patent: 5784944 (1998-07-01), Tozawa et al.
patent: 6006521 (1999-12-01), Fuchita et al.
patent: A 61-2908 (1986-01-01), None
patent: 61002908 (1986-01-01), None
patent: U 6-25601 (1994-04-01), None
patent: A 7-248004 (1995-09-01), None
patent: A 9-235756 (1997-09-01), None
Iga Makoto
Shimada Yoshiyuki
Kershteyn Igor
Look Edward K.
Oliff & Berridg,e PLC
Shin Caterpillar Mitsubishi Ltd.
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