Motors: expansible chamber type – With motive fluid valve – Plural separately controlled waste passages for single...
Patent
1997-02-18
1999-01-05
Ryznic, John E.
Motors: expansible chamber type
With motive fluid valve
Plural separately controlled waste passages for single...
91466, F15B 1108
Patent
active
058551590
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic circuit for supplying a pressurized discharge fluid from a hydraulic pump into a boom cylinder in a hydraulic shovel.
BACKGROUND ART
A hydraulic shovel has hitherto been known as shown, for example, in FIG. 1 of the drawings attached hereto. In such a hydraulic shovel, a lower vehicle body 2 that is equipped with a traveling body 1 has an upper vehicle body 3 mounted thereon as turnable, the said upper and lower vehicle bodies 2 and 3 constituting a vehicle body 4. A boom 5 is attached onto the said upper vehicle body 3 so as to be swung upwards and downwards by means of a boom cylinder 6. A forward end of the said boom 5 has an arm 7 attached thereto so as to be swung upwards and downwards by means of an arm cylinder 8. A forward end of the said arm 7 has a bucket 9 attached thereto so as to be turnable up and down by means of a bucket cylinder 10. Thus, the hydraulic shovel has been so configured that each of the boom 5 and the arm 7 may be swung upwards and downwards and the bucket 9 may be turned upwards and downwards, and has been used to perform an excavating operation.
A hydraulic circuit for such a hydraulic shovel is generally designed to supply a pressurized discharge fluid from a hydraulic pump into the boom cylinder 6, the arm cylinder 8 and the bucket cylinder 10 via a boom directional control valve, an arm directional control valve and a bucket directional control valve, respectively, to effect an extension and a retraction operation for each of these cylinders.
While an excavating operation is being carried out with a bucket with each of the cylinders expansion and retraction operated as shown in FIG. 1, it can be seen that if the load of excavation is increased due to the presence of a rock in the ground being excavated, the boom 5, the arm 7 and the bucket 9 will cease moving and will be made incapable of continuing the excavating operation. Then, it will become necessary to effect an extension operation for the boom cylinder 6 by acting on the boom directional control valve to swing the boom 5 upwards, thereby displacing the bucket 9 upwards.
Thus, since if a large load of excavation is encountered, it becomes necessary to operate the boom directional control valve to displace the bucket 9 upwards in the conventional hydraulic circuit, the operating efficiency has hitherto been poor and since the vehicle body is then flapped, the operation has also been burdensome for the operator.
In order to resolve these problems, it has been suggested that as shown in FIG. 1, a relief valve 14 having a low relief set pressure (relief-operating at a low pressure) should be provided in a circuit that connects the retraction pressure chamber 11 of the boom cylinder 6 to the boom directional control valve 12. The boom directional control valve 12 will then be switched from its neutral position a to its retraction position b to supply a pressurized discharge fluid of a hydraulic pump 15 into the retraction pressure chamber 11 of the boom cylinder 6. During an excavating operation, if the excavating load is increased whereby the pressure within the first circuit 13 reaches the above mentioned relief set pressure, the pressure fluid in the retraction pressure chamber 11 of the boom cylinder 6 will be allowed to flow out through the relief valve 14 into a reservoir 16. As a result, a situation may be eliminated in which the boom 5 will no longer be swung downwards, and the boom 5, the arm 7 and the bucket 9 will altogether cease moving.
If such a measure is undertaken, however, the pressure within the retraction pressure chamber 11 of the boom cylinder 6 can only be elevated up to the relief set pressure of the relief valve 14. Then, the force by which the boom 5 is swung downwards will be reduced.
For this reason, problems arise such as the inability to lift up the vehicle body 4 with one end portion 1a of the traveling body 1 serving as a supporting point by swinging the boom 5 downwards to press the bucket 9 against the ground surface and the
REFERENCES:
patent: 3948146 (1976-04-01), Maurer et al.
patent: 4282898 (1981-08-01), Harmon et al.
patent: 4794846 (1989-01-01), Von Der Ley et al.
patent: 5063742 (1991-11-01), Yoshimatsu
Honda Nobuhisa
Yoshida Nobumi
Kananen Ronald P.
Komatsu Ltd.
Ryznic John E.
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