Power plants – Pressure fluid source and motor – Having condition responsive control in a system of...
Patent
1990-10-12
1992-09-22
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of...
60430, 60422, 60486, 91 28, 91532, E02F 343, F16D 3102, F15B 1304
Patent
active
051486768
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a service valve circuit of a hydraulic excavator and, in particular, to a service valve circuit of a hydraulic excavator which has been connected beforehand for use in controlling a special attachment in addition to a prescribed actuator control valve.
DESCRIPTION OF THE RELATED ART
As shown in FIG. 3, a hydraulic excavator is generally equipped with a pivoting motor a in the upper chassis which is actuated by one or more units of variable capacity type hydraulic pumps (hereinafter referred to as a variable pump) driven by means of an engine, a boom cylinder b, an arm cylinder c and a bucket cylinder d for the control of a work machine, a hydraulic breaker e as a special attachment in place of the bucket, and a traveling motor f in the under traveling car. Most of the basic circuits of such a hydraulic excavator are as shown in FIG. 4. The following apparatuses are connected to two units of the variable pumps 2F and 2R driven by an engine 1 according to power distribution. That is, a left traveling control valve 4, a boom control valve 5, a bucket control valve 6, and a service valve 8F for controlling the hydraulic breaker e employed as a special attachment are connected to the inflow circuit 3F of the one variable pump 2F. To the inflow circuit 3R of the other variable pump 2R are connected a right traveling control valve 9, an arm control valve 10, a pivoting control valve 11, and a service valve 8R for controlling a special attachment.
There often arises a case in which a required quantity of flow in an actuator connected to the inflow circuit 3F of the variable pump 2F, for example, the boom cylinder b, must be backed up from the other variable pump 2R. As a confluence circuit in such a case, a control valve for confluence is required and this control valve is needed not only for the boom cylinder b but for each actuator. In the case of the service valves 8F and 8R, particularly, a great variety of special attachments can be installed. Therefore, the required quantity of flow differs in each case, and the confluence circuit needs to be so arranged that it can be used for the range from a small flow rate to a large flow rate. Hence, the service valves 8F and 8R should be connected to the inflow circuit 3F and 3R of both the variable pumps 2F and 2R. For example, where the hydraulic breaker e is installed in the service valve 8F of the inflow circuit 3F and a required quantity of flow must be backed up from the other variable pump 2R, a control valve 12 for confluence must be disposed beforehand as its confluence circuit.
In such service valve circuits, the service valves 8F and 8R, the frequency of whose use is relatively low, must be connected to the inflow circuits 3F and 3R of both the variable pumps. In addition, the service valve circuit is uneconomical and complex owing to the fact that the control valve 12 for confluence must be disposed beforehand according to a required quantity of flow. The control valve 12 for confluence performs only on-off control with an opening and closing valve and control of the confluent flow rate cannot be exercised. Therefore, the flow rate is adjusted using the number of rotations of an engine. This method of control causes inconveniences such that when it is switched from a special attachment control to a pivoting or traveling control, the action is slowed down.
SUMMARY OF THE INVENTION
The present invention has been devised in light of the above-mentioned circumstances. Accordingly, it is an object of the present invention to provide a service valve circuit of a hydraulic excavator, in which an excessive quantity of confluence is not needed, by setting in advance the requirement of confluence with respect to a required quantity of flow for a special attachment and the quantity of confluence, and which will not be slowed down even if switched from a special attachment control to a pivoting or traveling control without adjusting the quantity of flow using the number of rotations of an engine.
According
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Moriya Yukio
Onoda Takumi
Takamura Fujitoshi
Yokoyama Toshio
Kabushiki Kaisha Komatsu Seisakusho
Look Edward K.
Ryznic John
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