Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Patent
1991-04-01
1993-03-30
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
60451, 60488, 60493, F16D 3102, F16D 3900
Patent
active
051972832
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to hydraulic-motor drive circuit systems and, more particularly, to a hydraulic-motor drive circuit system which is provided in a construction machine such as, for example, a hydraulic excavator or the like and which is suitable for drivingly controlling a traveling hydraulic motor.
BACKGROUND ART
As disclosed, for example, in JP, U, 62-19475, a conventional traveling hydraulic-motor drive circuit system, which is used in a construction machine such as a hydraulic excavator or the like, comprises a hydraulic motor whose output shaft is connected to a traveler such as, for example, a crawler or the like, for rotatively driving a vehicle body which is an inertia load, a hydraulic pump serving as a main hydraulic source, a reservoir, a pair of main lines through which the hydraulic motor is connected to the hydraulic pump and the reservoir, and a directional control valve of normal open type arranged in the pair of main lines for switching a direction of hydraulic fluid supplied to the hydraulic motor from the hydraulic pump. further, a counter balance valve is arranged in the pair of main lines between the directional control valve and the hydraulic motor.
The counter balance valve comprises a pair of check valves, a pressure control valve arranged in parallel to the check valves and normally biased to a neutral position under biasing forces of springs, the pressure control valve being switched from the neutral position to left- and right-hand operative positions against the biasing forces of the springs when the hydraulic fluid from the hydraulic pump acts as pilot pressure, and a pair of restrictors for regulating or adjusting the switching speed of the pressure control valve. The pressure control valve is provided with intermediate restriction regions at respective locations between the neutral position and the operative positions, whereby when the pressure control valve is returned to the neutral position from the operative positions, a restriction action is given to return fluid from the hydraulic motor to generate brake pressure in the main line on the return side.
In the hydraulic-motor drive circuit system constructed as described above, when the directional control valve is switched to the operative positions from the neutral position, the hydraulic fluid from the hydraulic pump is supplied to the hydraulic motor through the directional control valve, one of the main lines and the corresponding check valve to rotate the hydraulic motor together with the inertial load. At this time, pressure within the main line (drive pressure of the hydraulic motor) on the outlet side of the directional control valve acts as pilot pressure on the pressure control valve of the counter balance valve through one of the restrictors. The pressure control valve is switched from the neutral position to the operative positions by the pilot pressure. Thus, the return fluid from the hydraulic motor is discharged to the reservoir through the other main line.
On the other hand, when the vehicle reaches a downward path or the like under the condition that the hydraulic motor is rotated together with the inertia load and then the hydraulic motor is caused to rotate by the inertia load, pressure within the main line on the supply side is reduced by a pump action of the hydraulic motor so that the pressure control valve of the counter balance valve tends to be returned to the neutral position from the operative positions through one of the restriction regions. Accordingly, the return fluid from the hydraulic motor is confined within the main line on the return side at a location between the hydraulic motor and the counter balance valve. Thus, the pressure in the main line on the return side is raised to a setting pressure of an overload relief valve which is provided in the pair of main lines, and brake pressure is generated in the main line on the return side, thereby preventing the vehicle from scampering at the downward path or the like.
Further, when the directional control val
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Kagiwada Hitoshi
Yasuoka Tomohiko
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Ryznic John
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