Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Patent
1998-11-24
2000-09-05
Ryznic, John E.
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
91461, F16D 3102, F15B 1108
Patent
active
061125210
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a backpressure control circuit for a hydraulic drive device and, more particularly, to a backpressure control circuit which can change a backpressure of a hydraulic drive device for supplying a pressurized oil, discharged from a hydraulic pump, to a hydraulic traveling motor in a hydraulic drive-type travel vehicle, such as a construction machine or the like, and for driving the motor.
BACKGROUND ART
In order to drive a hydraulic traveling motor in a hydraulic drive-type travel vehicle, oil, discharged from a hydraulic pump, is switched by a direction changeover valve and is subsequently supplied to one of the two ports of the hydraulic motor. Return oil flows from the other port of the hydraulic motor to a tank via the direction changeover valve, and rotationally drives the hydraulic motor in one direction, for example the forward direction or the backward direction, or in the other direction to drive a traveling body.
In the meantime, when the hydraulic drive type travel vehicle goes downhill, the drive wheels are rotated by gravity acting on the vehicle, and the hydraulic motor is inversely driven by the drive wheels, so that the hydraulic drive type travel vehicle descends rapidly. In such a case, the hydraulic motor needs to be braked and stopped.
Accordingly, two of the present inventors and another proposed a drive device for a hydraulic motor in an unpublished Japanese Patent Application No. 7-065718. The unpublished proposal will be described with reference to FIGS. 8 and 9. Specifically, a directional control valve (a direction changeover valve) is a pilot pressure changeover type, and a pilot pressure supply valve is provided for supplying a pressure of a main circuit as a pilot pressure to a pressure receiving element of the directional control valve. When the hydraulic motor is inversely driven by an external force, such as a traveling body and the like, the pressure of the main circuit is lowered, whereby the pilot pressure is lowered so that the directional control valve is switched to its neutral position to give a braking force to the hydraulic motor. When the directional control valve is in its neutral position, a predetermined pressure is supplied to the main circuit, thus securing the pilot pressure and preventing cavitation at the time of braking and stopping.
In other words, as shown in FIG. 8, a pilot pressure supply valve 37, which is switched to its first position G or its second position H in accordance with a command from a final control element 38, is provided. A directional control valve 30 is switched to its first position B or its second position C upon receipt of the pressure of the first main circuit 21 or the pressure of the second main circuit 22 of a hydraulic motor 24, either of which passed through the pilot pressure supply valve 37. When the directional control valve 30 is switched to its first position B, pressurized oil discharged from the hydraulic pump 20, flows into the first port 25 of the hydraulic motor 24 via the first main circuit 21, and return oil flows from the second port 26 into the tank 27 via the second main circuit 22, the directional control valve 30, and the backpressure valve 35, so that the hydraulic motor 24 is rotationally driven in one direction (indicated by the arrow D). Also when the directional control valve 30 is switched to its second position C, the hydraulic motor 24 is rotationally driven in the other direction (indicated by the arrow E) in the same way as above.
As described above, when the hydraulic motor 24 is inversely driven by an external force, such as a traveling body and the like, while being rotationally driven, the pressure of the first main circuit 21 or the second circuit 22 is reduced so that the directional control valve 30 is switched to its neutral position A, where the first check valve 31 and the second check valve 32 prevent pressurized oil from the first port 25 and the second port 26 of the hydraulic motor 24 from flowing into the tank 27, so that the hydraulic
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Hayashi Seita
Kado Hideki
Nunotani Sadao
Komatsu Ltd.
Ryznic John E.
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