Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
2001-07-19
2003-09-16
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S430000
Reexamination Certificate
active
06619037
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydraulic drive system for a civil engineering or construction machine such as a hydraulic excavator, which is suitable for arrangement in the civil engineering or construction machine and has a first control valve group connected to a first hydraulic pump and including plural directional control valves and a second control valve group connected to a second hydraulic pump and including plural directional control valves.
BACKGROUND ART
As conventional art of this type, there is, for example, one disclosed in JP 2642972 B2. This conventional art relates to a hydraulic circuit for a civil engineering or construction machine, and is provided with a first hydraulic pump and a second hydraulic pump.
Connected to the first hydraulic pump is a first control valve group, which is provided on a most downstream side with a bypass on/off valve having an open position and a closed position for selectively maintaining a bypass passage in or out of communication and makes up a single housing including a revolving-controlling directional control valve, an arm-controlling directional control valve, and a travel-controlling directional control valve for one of traveling motors. The individual directional control valves in this first control valve group are connected parallel to the first hydraulic pump.
Connected to the second hydraulic pump is a second control valve group, which makes up another housing including, in addition to a reserve directional control valve as an attachment-controlling directional control valve for controlling an attachment actuator for driving an attachment such as a hydraulic breaker or a hydraulic venchure, a boom-controlling directional control valve, a bucket-controlling directional control valve, and a travel-controlling directional control valve for the other traveling motor. The individual directional control valves in this second control valve group, except for the reserve directional control valve, are connected parallel to the second hydraulic pump.
Further, a communication line is arranged to communicate a delivery line from the first hydraulic pump and a supply line to the reserve directional control valve with each other. This communication line is connected at one end thereof to the housing of the first control valve group and at an opposite end thereof to the housing of the second control valve group. In other words, the communication line is arranged as an external piping outside the respective housings.
In addition, a shuttle valve is also arranged. The shuttle valve detects a pilot pressure which serves to change over the reserve directional control valve, and the shuttle valve takes it out as a control pressure for changing over the above-mentioned bypass on/off valve to the closed position.
When the reserve directional control valve is changed over in the conventional art constructed as described above, its operating pressure is applied as a control pressure to a drive portion of the bypass on/off valve in the first control valve group via the shuttle valve, and the bypass on/off valve is changed over to the closed position. Pressure oil from the first hydraulic pump is, therefore, supplied to the communication line arranged outside the two housings. This pressure oil is supplied further to the reserve directional control valve, and then to the attachment actuator controlled by the reserve directional control valve. Accordingly, the attachment actuator controlled by the reserve directional control valve is driven by the pressure oil from the first hydraulic pump rather than pressure oil from the second hydraulic pump connected to the second control valve group to which the reserve directional control valve belongs.
In the above-mentioned conventional art, the communication line through which the pressure oil from the first hydraulic pump is guided to the reserve directional control valve is a line arranged outside the housings in which the first control valve group and the second control valve group are accommodated, respectively, in other words, is an external line. The communication line, therefore, tends to become longer, leading to problems that a pressure loss tends to become large and the accuracy of control of attachment actuators tends to drop.
Further, the above-mentioned communication line is connected at the one end thereof to the housing in which the first control valve group is accommodated and at the opposite end thereof to the housing in which the second control valve group is accommodated. Oil leakage, therefore, tends to occur at both of the connected parts. Occurrence of such oil leakage leads to insufficiency in the amount of oil in the circuit and also to contamination of surrounding equipment with the oil.
Additional work is required to connect the one end of the communication line to the housing in which the first control valve group is accommodated and also to connect the opposite end of the communication line to the housing in which the second control valve group is accommodated. Accordingly, assembly work of the hydraulic circuit, that is, the hydraulic drive system becomes irksome, thereby leading to a reduction in the efficiency of the assembly work.
In the above-mentioned conventional art, it is only the pressure oil delivered from the first hydraulic pump that is supplied to the reserve directional control valve. The operating speed of the attachment actuator controlled by the reserve directional control valve is, therefore, limited in a wholesale manner to a slow speed (the first speed). It is, therefore, impossible to change the maximum value of the operating speed of the attachment actuator, for example, to set the operating speed of the attachment actuator at two speeds consisting of a slow speed and a fast speed. This has led to a problem that no improvement can be expected in the efficiency of work to be performed by the operation of the attachment actuator.
The present invention has been completed in view of the above-described circumstances of the conventional art, and a first object of the present invention is to provide a hydraulic drive system for a civil engineering or construction machine, which can shorten the length of a communication line through which a hydraulic pump, which is arranged to supply pressure oil to a control valve group in which no reserve directional control valve is included, and a reserve directional control valve are connected with each other, can prevent oil leakage from the communication line, can obviate connection work for the communication line, and can change the maximum value of the operating speed of the actuator controlled by the reserve directional control valve.
A second object of the present invention is to provide a hydraulic drive system for civil engineering or construction machine, which can change the maximum value of the operating speed of an actuator controlled by a reserve directional control valve and can also achieve good combined operation of the actuator, which is controlled by the reserve directional control valve, and an actuator which is controlled by a specific directional control valve belonging to a control valve group without the reserve directional control valve and may be applied with a load pressure higher than a load pressure too the actuator controlled by the reserve directional control valve.
DISCLOSURE OF THE INVENTION
To achieve the above-described first object, the present invention provides in a first aspect thereof a hydraulic drive system for a civil engineering or construction machine, said system being provided with a first hydraulic pump and a second hydraulic pump, a first control valve group connected to the first hydraulic pump, provided on a most downstream side thereof with a bypass on/off valve having an open position and a closed position for selectively maintaining a bypass passage in or out of communication, and a second control valve group connected to the second hydraulic pump and comprised of plural directional control valves including a reserve directional control valve, characterized
Hirata Toichi
Ishikawa Kouji
Nakamura Tsuyoshi
Nishimura Masao
Sugiyama Genroku
Crowell & Moring LLP
Hitachi Construction Machinery Co. Ltd.
Lopez F. Daniel
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