Fluid handling – Systems – Supply and exhaust
Patent
1998-09-17
1999-09-28
Michalsky, Gerald A.
Fluid handling
Systems
Supply and exhaust
60427, 60452, 91447, 91518, 13759613, F15B 1308
Patent
active
059571594
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a directional control valve with flow distribution valves, and more particularly to a directional control valve with flow distribution valves, which is used in a hydraulic circuit for operating a plurality of actuators in a construction machine such as a hydraulic excavator, thereby ensuring a distribution characteristic during the combined operation.
BACKGROUND ART
For supplying a hydraulic fluid delivered from a hydraulic pump to a plurality of hydraulic actuators, it is conventional to provide a plurality of directional control valves in a delivery line of the hydraulic pump and shift the directional control valves selectively so that the hydraulic fluid is supplied to desired one of the hydraulic actuators. With this arrangement, however, when the hydraulic fluid is supplied to several hydraulic actuators at the same time, the hydraulic fluid is supplied to only the hydraulic actuator under a smaller load, and no hydraulic fluid is supplied to the hydraulic actuator under a larger load.
JP, B, 4-48967 and U.S. Pat. No. 5,305,789, for example, propose hydraulic circuits for overcoming such a problem.
In the hydraulic circuit proposed in JP, B, 4-48967, a plurality of directional control valves are provided in a delivery line of a hydraulic pump, and a pressure compensating valve for varying a setting differential pressure depending on a load sensing differential pressure (i.e., a differential pressure between a maximum load pressure among the plurality of directional control valves and a delivery pressure of the hydraulic pump) is provided in a circuit section between the hydraulic pump and a variable throttle of each of the directional control valves. The pressure compensating valve controls a differential pressure across the variable throttle.
In the hydraulic circuit proposed in U.S. Pat. No. 5,305,789, a plurality of directional control valves are provided in a delivery line of a hydraulic pump, and a pressure control valve responsive to a maximum load pressure is provided in a circuit section between a variable throttle of each of the directional control valves and each corresponding hydraulic actuator. The pressure control valve controls a pressure on the outlet side of the variable throttle to be kept substantially at the maximum load pressure.
Hereunder, the pressure compensating valve disclosed in JP, B, 4-48967 is referred to as the prepositional type and the pressure control valve disclosed in U.S. Pat. No. 5,305,789 is referred to as the postpositional type. Further, the prepositional type pressure compensating valve is referred to as a variable pressure compensating valve and the postpositional type pressure control valve is referred to as a flow distribution valve.
To effect the function of the variable pressure compensating valve or the flow distribution valve, the maximum load pressure is detected with a shuttle valve or the like and introduced to a signal line.
FIG. 12 shows the hydraulic circuit proposed in JP, B, 4-48967. A maximum load pressure detected by a shuttle valve 237 is output to a signal line 238. The maximum load pressure is transmitted through signal lines 239, 241 from the signal line 238 to one ends of variable pressure compensating valves 206, 216 provided respectively between a hydraulic pump 201 and directional control valves 208, 218.
When the maximum load pressure is transmitted in such a way, the variable pressure compensating valves 206, 216 operate so that the relationship of; in line 225 upstream of variable throttle)--(pressure in line 224 downstream of variable throttle) of; in line 227 upstream of variable throttle)--(pressure in line 226 downstream of variable throttle) pressure in line 239)=(maximum load pressure in line 241) control valves 208 and 218 are equal to each other.
Accordingly, even when a difference in load pressure exists between hydraulic actuators 212 and 222, a delivery rate of the hydraulic pump 201 is distributed depending on an opening area ratio between the variable throttles, and he
REFERENCES:
patent: 3881512 (1975-05-01), Wilke
patent: 5305789 (1994-04-01), Rivolier
patent: 5315826 (1994-05-01), Hirata et al.
Aoki Minoru
Ichiki Nobuhiko
Nishimura Yoshizumi
Nozawa Yusaku
Takahashi Kinya
Hitachi Construction Machinery Co. Ltd.
Michalsky Gerald A.
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