Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Reexamination Certificate
1999-03-04
2001-12-18
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
C060S486000
Reexamination Certificate
active
06330797
ABSTRACT:
SPECIFICATION
1. Field of the Art
The present invention r elates to a hydraulic circuit system having at least three hydraulic pumps for supplying hydraulic actuators of a turning excavator with pressure oil, wherein working arms consisting of a boom, an arm and a bucket are operated and a turning excavator body is turned by the respective hydraulic actuators.
2. Background Art
Conventionally, it is a well-known technique for a turning excavator having a turning excavator body (a main body) and working arms consisting of a boom, an arm and a bucket to provide the hydraulic circuit system thereof with three hydraulic pumps for supplying hydraulic actuators for respectively driving the boom, the arm, the bucket and the main body with pressure oil, wherein each actuator is supplied with pressure oil by one of the pumps whether the actuators are driven one by one at different times (individually) or more than one of those are driven simultaneously.
For increasing the operation speed of each of the working arms like the boom, Japanese Laid Open Gazette No. Hei 8-134960 discloses a conventional turning excavator provided with a purpose-built hydraulic circuit having a hydraulic pump for it, wherein the circuit can be joined with chosen one of hydraulic circuits for the respective hydraulic actuators like a boom cylinder. Furthermore, Japanese Laid Open Gazette No. Hei 8-113961 discloses a joining circuit including a check valve interposed between a hydraulic circuit for turning the main body and a hydraulic circuit for driving the boom, thereby making the erecting operation of the boom faster than the turning operation of the main body when they are driven simultaneously.
Especially in various operations of the boom, the arm and the bucket of the working arms for excavation, the erecting operation of the boom and the pulling operation of the arm are hoped to be as swift as possible. However, with respect to the conventional hydraulic system, each hydraulic actuator is supplied with pressure oil from a single hydraulic pump, thereby being too low in quantity of pressure oil to be operated at such a hopeful speed. The hydraulic circuit system disclosed in Japanese Laid Open Gazette No. Hei 8-134960 is further provided with such purpose-built circuit for increasing the operation speed, thereby being complicated and expensive. Moreover, the check valve in the joining circuit cannot limit the amount of joined oil flow for restricting the increasing of the operation speed.
In some working conditions, more than one of the main body and the working arms are driven simultaneously. For example, a horizontal motion of the bucket for horizontal excavation requires the simultaneous erecting operation of the boom and pulling operation of the arm. In this case, making the pulling operation of the arm faster than the erecting operation of the boom is effective. However, there is no conventional hydraulic circuit system designed with said case in mind so as to give the arm priority over the boom when the both are operated simultaneously.
Supposing the turning excavator raises sand and moves it to a truck, the erecting operation of the boom must be prior to the turning of the main body. The above said conventional hydraulic circuit system of Japanese Laid Open Gazette No. Hei 8-113961 is designed with this situation in mind. However, one of the three hydraulic pumps thereof is for pilot operation, so that each actuator is substantially supplied with pressure oil from either of only the other two pumps. Also, supposing a small excavator employs this hydraulic circuit system, the hydraulic pressure for turning operation of the main body is to be limited low. However, as the pressure oil for turning the main body flows into the hydraulic circuit for driving the boom, the boom may be moved too fast. The operation speed of the boom cannot be limited because the oil flowing from the above said joining circuit to the hydraulic circuit for the hydraulic actuator for the boom cannot be shut off.
SUMMARY OF THE INVENTION
A hydraulic circuit for a turning excavator according to the present invention is provided with first, second and third hydraulic pumps for supplying pressure oil to respective hydraulic actuators for driving a boom, an arm, a bucket and a turning main body of the turning excavator.
During the individual driving of them, an actuator for the boom is supplied with pressure oil from the first and third pumps, an actuator for the arm from the second and third pumps, an actuator for the bucket from the first pump, and an actuator for the main body from the third pump.
For simultaneously driving the boom and the arm, the third pump supply pressure oil to the actuator for the arm prior over that for the boom.
During the simultaneous driving of the boom and the arm, the hydraulic circuit, which makes the above mentioned pressure oil supplying patterns by the first, second and third hydraulic pumps thereof, preferentially supplies the actuator for the arm with pressure oil from the third pump. When the boom and the main body are operated simultaneously, it additionally supplies the actuator for the boom with a part of the pressure oil to the actuator for the main body from the third pump through a branching circuit.
The branching circuit toward the actuator for the boom may be a bleed-off-circuit.
Additionally, the pressure oil from the third pump to the actuator for the arm is partly bled off.
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Ryznic John E.
Sterne Kessler Goldstein & Fox P.L.L.C.
Yanmar Diesel Engine Co. Ltd.
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