Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1993-12-14
1996-01-23
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60452, 71 6, F16D 3102
Patent
active
054857244
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic drive system equipped on civil engineering and construction machines such as hydraulic excavators, and more particularly to a hydraulic drive system comprising a plurality of variable restrictors for controlling respective flow rates supplied to a plurality of actuators and a plurality of pressure compensating valves for controlling respective differential pressures across the plurality of variable restrictors, maximum one of load pressures of the plural actuators being selected as a maximum load pressure and applied as a signal pressure to a regulator for a variable displacement hydraulic pump.
BACKGROUND ART
As civil engineering and construction machines, e.g., hydraulic excavators, there is known the type of machine that includes a plurality of actuators such as a boom cylinder, an arm cylinder, a bucket cylinder, a travel motor and a swing motor, and a hydraulic drive system for supplying a hydraulic fluid to those actuators includes a plurality of variable restrictors in communication with a delivery line of a hydraulic pump, the variable restrictors being operated to supply the hydraulic fluid to the corresponding actuators. However, without operation of such a hydraulic drive system there is a fear that when plural variable restrictors are operated simultaneously, the hydraulic fluid is supplied to the actuator having a small load pressure, but not supplied to the actuator having a large load pressure.
For that reason, there has been proposed a hydraulic drive system as disclosed in JP, A, 2-248705. This prior-art system comprises first and second variable displacement hydraulic pumps, a first hydraulic actuator driven by hydraulic fluids delivered from the first and second hydraulic pumps, a second hydraulic actuator driven by the hydraulic fluid delivered from the second hydraulic pump, a first variable restrictor for controlling a flow rate of the hydraulic fluid supplied from the first hydraulic pump to the first hydraulic actuator, a second variable restrictor for controlling a flow rate of the hydraulic fluid supplied from the second hydraulic pump to the first hydraulic actuator, a third variable restrictor for controlling a flow rate of the hydraulic fluid supplied from the second hydraulic pump to the second hydraulic actuator, a first pressure compensating device for controlling a differential pressure across the first variable restrictor, a second pressure compensating device for controlling a differential pressure across the second variable restrictor, a third pressure compensating device for controlling a differential pressure across the third variable restrictor, a first regulator for controlling a delivery rate of the first hydraulic pump, a second regulator for controlling a delivery rate of the second hydraulic pump, and a coupling circuit for joining the flow rate passing through the first variable restrictor and the flow rate passing through the second variable restrictor with each other and supplying the joined flow rate to the first hydraulic actuator.
The above prior-art system further comprises a first check valve for detecting a pressure on the outlet side of the first pressure compensating device, a second check valve for detecting a pressure on the outlet side of the second pressure compensating device, a third check valve for detecting a pressure on the outlet side of the third pressure compensating device, and a signal pressure supply circuit for selecting maximum one of the pressure detected by the first check valve, the pressure detected by the second check valve and the pressure detected by the third check valve, and supplying the selected maximum pressure as a common signal pressure to the first and second regulators.
The first and second variable restrictors, the first and second pressure compensating devices, and the first and second check valves constitute one valve apparatus. Also, the first and second variable restrictors are formed in a common slidable spool.
In the case of solely driving the first
REFERENCES:
patent: 4087968 (1978-05-01), Bianchetta
patent: 4367624 (1983-01-01), Ogata et al.
patent: 4425759 (1984-01-01), Krusche
patent: 4759183 (1988-07-01), Kreth et al.
Ichiki Nobuhiko
Ino Kazuyuki
Matsuzaki Hiroshi
Nozawa Yusaku
Ohtsu Wataru
Hitachi Construction Machinery Co. Ltd.
Lopez F. Daniel
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