Motors: expansible chamber type – With motive fluid valve – Relatively movable serial valves
Patent
1990-07-12
1991-11-05
Kwon, John T.
Motors: expansible chamber type
With motive fluid valve
Relatively movable serial valves
91446, 91461, 60427, 414699, F15B 1108
Patent
active
050623508
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a hydraulic drive system for civil engineering and construction machines such as hydraulic excavators, and more particularly to a hydraulic drive system for civil engineering and construction machines in which a hydraulic fluid is distributed and supplied from a hydraulic pump via a plurality of pressure compensating valves and flow control valves to a plurality of associated actuators, including an arm cylinder and a boom cylinder, for simultaneously driving those actuators to perform the desired combined operation.
2. Background Art
A hydraulic excavator is one example of a civil engineering and construction machine in which a plurality of actuators including an arm cylinder and a boom cylinder are simultaneously driven to perform the desired combined operation. Such a hydraulic excavator comprises a lower travel body for moving the hydraulic excavator, an upper swing which is swingably mounted on the lower travel body, and a front mechanism consisted of a boom, an arm and a bucket. Various equipment such as a cab, prime mover and a hydraulic pump are mounted on the upper swing to which is also attached the front mechanism.
As a hydraulic drive system for use in that type civil engineering and construction machine, there is known a system, called a load sensing system, in which the pump delivery rate is controlled to hold a delivery pressure of the hydraulic pump higher a fixed value than a maximum load pressure among the plurality of actuators, causing the hydraulic pump to deliver the hydraulic fluid at a flow rate necessary for driving the actuators. This load sensing system typically includes, as disclosed in JP, A, 60-11706, a pump regulator comprising a selector valve operated responsive to both the delivery pressure of the hydraulic pump and the maximum load pressure among the plurality of actuators extracted through a detection line for controlling supply and discharge of the hydraulic fluid, and a working cylinder controlled in its operation by the hydraulic fluid controlled by the selector valve to vary the displacement volume of the hydraulic pump. The selector valve is provided with a spring for urging the selector valve in the direction opposite to a differential pressure between the pump delivery pressure and the maximum load pressure. In the pump regulator, when the maximum load pressure is raised, the selector valve is operated to drive the working cylinder, whereupon the displacement volume of the hydraulic pump is made greater for increasing the pump delivery rate larger and hence the pump delivery pressure. The pump delivery pressure is thereby controlled to be held higher than the maximum load pressure by a predetermined value decided by the spring.
Furthermore, in the load sensing system, a pressure compensating valve is generally disposed upstream of each flow control valve. This permits a differential pressure across the flow control valve to be held at a predetermined value decided by a spring of the pressure compensating valve. By thus arranging the pressure compensating valve to hold the differential pressure across the flow control valve at the predetermined value, when a plurality of actuators are simultaneously driven, the differential pressures across the flow control valves associated with all the actuators can be held at the predetermined value. It is therefore possible to precisely perform flow rate control for all the flow control valves irrespective of fluctuations in load pressures, allowing the plural actuators to be simultaneously driven at desired drive speeds in a stable manner.
In the load sensing system disclosed in JP, A, 60-11706, means for applying the pump delivery pressure and the maximum load pressure in directions opposite to each other is provided in place of the spring of each pressure compensating valve, so as to set the above predetermined value in accordance with the differential pressure therebetween. As mentioned above, the differential pressure between the pump delivery pressure and t
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patent: 3911942 (1975-10-01), Becker
patent: 4369625 (1983-01-01), Izumi et al.
patent: 4753158 (1988-01-01), Hirata et al.
patent: 4875337 (1989-10-01), Sugiyama et al.
patent: 4967557 (1990-11-01), Izumi et al.
Haga Masakazu
Hirata Toichi
Kajita Yusuke
Sugiyama Genroku
Tanaka Hideaki
Hitachi Construction Machinery Co. Ltd.
Kwon John T.
Mattingly Todd
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