Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
2001-06-26
2003-05-13
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C060S468000
Reexamination Certificate
active
06560962
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a control system of a construction machine such as a hydraulic excavator and the like, and specifically to an control system for controlling the flow rate of the hydraulic fluid which is drained to a reservoir across a variable bleed valve for developing the drive speed of each hydraulic actuator for the purpose of a high responsibility and stability when a work implement starts to be driven.
BACKGROUND OF THE INVENTION
Various methods for providing the stability of a work implement drive speed have been conventionally proposed. An abrupt increasing flow rate when a main pump starts to he driven, as shown with a full line in
FIG. 6
, for example, can be controllably restrained by sacrificing partially the responsibility of a hydraulic pump, or performing a bleed-of f control of main spool of a flow control valves, or disposing associated with fixed or variable orifice in each load sensing signal line through which regulates the displacement of hydraulic main pump. In order to restrain the flow rate of the hydraulic fluid from the hydraulic main pump from increasing abruptly when the work implement starts to be driven as dotted line shown in
FIG. 6
, with the above methods, there is provided troubles that slow drive speed (P) of the hydraulic actuator causes the work implement to lead to as low rise action during operation, that is to say, a poor responsibility and provides a poor efficiency in the hydraulic control system. To handle with these problems, the use of a high main pump in efficiency or the elimination of the orifices disposed in load sensing signal lines have been performed for over coming the above-described troubles. It could be well understood that such a approach has another problem that as shown a one dot line in
FIG. 6
, the drive speed of the work implement actuator increases abruptly when it starts to be driven (Q) and also a potential hunting (R) of the work implement.
For the purpose of providing for coexisting with the contrary characteristics, that is to say, responsibility and stability of hydraulic control system, Japanese published patent No. 2000-35005 assigned to the assignee of the present invention, proposed for providing an control system for enhancing the stability in a load speed even if the hydraulic main pump with a high responsibility is used in the hydraulic control system. Disclosed is that a control system of the hydraulic drive construction machine which comprises a bleed-off circuit which exhaust the detection pressure line supplied to a hydraulic actuator through the flow control valve from the displacement type hydraulic main pump, a variable bleed valve disposed in the bleed-off circuit so that the hydraulic fluid through a flow control valve to a reservoir is possibly controlled to exhaust, and a controller for determining an amount of the exhausted fluid through the bleed valve in response to delivery pressure of the hydraulic main pump. With such construction, the prior bleed-off control circuit has provided for a high stability in the respective drive speed of each hydraulic actuator of the work implement without depending on the spool stroke of the flow control valve or an amount of a manually operable lever stroke.
This type of hydraulic construction machine can be generally used to carry out the various type of works, for example, a digging work which the bucket mounted pivotally at free end of the arm is pushed against the each side portion of a trench by actuating the boom hydraulic actuator and the arm hydraulic actuator while the operating lever is set at the position that the work implement mounted on the frame can turn, a land grinding work forwards and rearwards, and the like, except a digging work. It could be noted that the responsibility and stability in the work implement drive speed should be respectively varied depending on the desired characteristics for the types of work when the work implement starts to be driven. However, the prior foregoing flow control has a drawback that since the flow amount of the hydraulic fluid through the variable bleed valve to the reservoir is absolutely determined based on the delivery pressure of the hydraulic main pump. With thus construction, it was impossible that a suitable characteristic required for the respective type of work completely provides for ensuring efficiently for the respective type of work.
The present invention is to overcoming the problems set forth above. An object of the present invention is to provide a hydraulic control system of the hydraulic drive excavator for ensuring the stability of the work implement by eliminating an abrupt movement of the work implement actuator while a high responsibility of the work implement being ensured when it starts to be driven.
Another object of the present invention is to provide a hydraulic construction machine which provides a control system for ensuring the optimum characteristic required for respective type of work through a monitor.
DISCLOSURE OF THE INVENTION
In order to achieve the above object, according to the first invention, there is provided a control system of a hydraulic construction machine including a variable displacement type hydraulic pump, a hydraulic actuator driven by hydraulic fluid from the main pump, a flow control device for controllably supplying a flow of the hydraulic fluid to the hydraulic actuators from the main pump in response to an amount of a manually operable lever stroke, or a spool stroke thereof, a variable bleed valve disposed in a bleed-off hydraulic circuit through which the hydraulic fluid exhausts to a reservoir, and a controller for regulating an opening area of the variable bleed valve, is characterized in that said controller includes a storage unit containing a plurality of functions as an opening area function which determines the optimum flow amount of the hydraulic fluid through the variable bleed valve, and a selecting means such as a monitor is connected to the controller so that the desired opening area function among plural functions can be generated and transmitted to the controller.
With the first invention, there is provided the bleed-off circuit for exhausting the hydraulic fluid which flows to hydraulic actuator through the flow control device, the bleed-off circuit including a variable bleed valve which determines the opening area thereof or the amount of the hydraulic exhausted fluid to the reservoir in response of external command signals from the controller of the variable bleed valve. With thus arranged, there is provided the selecting means such as the monitor generating an external command signal and transmitting to the controller of the variable bleed valve in order to select the desired opening area function among a plurality of the types of works such as “Heavy Power Mode”, “General Standard Power Mode” and “Light Power Mode” and the like, which is respectively stored in the storage unit. The optimum opening function required for the selected type of work is read out in responsive to the selected command signal from the external monitor and the like. With thus, this brings to obtain the optimum characteristic or a high responsibility and stability to meet with the desired characteristic for the selected type of work.
In the second invention according to the first invention, a storage unit containing a plurality of functions as an opening area function which determines the optimum flow amount of the hydraulic fluid through a variable bleed valve is characterized in that the storage unit has a plurality of data maps which are made based on the associated plural opening areas of the variable bleed-off correlated with the delivery pressure of the hydraulic main pump.
In the third invention according to the first invention, a storage unit containing a plurality of functions as an opening area function which determines the optimum flow amount of the hydraulic fluid through the variable bleed valve is characterized in that the storage unit have a plurality of data maps which are made based on the associa
Fuchita Seiichi
Kawamura Kouichi
Sawada Hiroshi
Komatsu Ltd.
Lazo Thomas E.
Varndell & Varndell PLLC
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