Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Patent
1991-02-28
1993-04-20
Smith, Leonard E.
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
91446, 13759613, 251285, 60452, F04B 126
Patent
active
052036782
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a valve apparatus for use in a hydraulic drive system for civil engineering and construction machines such as hydraulic excavators and cranes, as well as a hydraulic drive system equipped with the valve apparatus, and more particularly to a valve apparatus for use in a hydraulic drive system including a hydraulic fluid supply source which has a supply pressure control function such as a load sensing system, and also a hydraulic drive system for the valve apparatus.
BACKGROUND ART
In a hydraulic drive system for civil engineering and construction machines such as hydraulic excavators and cranes, a flow of a hydraulic fluid supplied from a hydraulic fluid supply source to an actuator is controlled by a valve apparatus including a flow control valve.
This type hydraulic drive system uses, as a hydraulic fluid supply source, means for controlling the supply pressure to be held higher a fixed value than the load pressure of the actuator. As disclosed in GB 2195745A, one example of such means is a pump regulator which implements a load sensing system for controlling the pump delivery rate such that the delivery pressure of a hydraulic pump is higher a fixed value than the load pressure. Because the hydraulic fluid is supplied with the load sensing system just at a flow rate required by the actuator, undesired supply of the hydraulic fluid is reduced, which is advantageous in economy. On the other hand, the load sensing system also has the shortcoming that the pump delivery pressure cannot be controlled after the intention of an operator because of its dependency on the load pressure. Therefore, when an inertial load such as a swing of hydraulic excavators is turned, the pump delivery pressure increases up to the setting pressure of a main relief valve irrespective of the amount of a flow control valve operated. This raises the problem that an acceleration of the inertial load is maximized and the operator suffers from a large shock.
A known one of valve apparatus for use in the hydraulic drive system implementing the above load sensing system is disclosed in JP, A, 61-88002. This disclosed valve apparatus comprises a flow control valve having a supply passage communicating with a hydraulic fluid supply source, a load passage communicating with an actuator, and a first meter-in variable restrictor disposed between the supply passage and the load passage and opened dependent on an operation amount thereof; a first signal passage branched from the load passage downstream of the first variable restrictor and including a restrictor and a check valve allowing a hydraulic fluid to flow toward the load passage; a tank passage communicating with a reservoir tank; a discharge passage for communicating the first signal passage with the tank passage; a second variable restrictor provided in the discharge passage and having its opening variable dependent on the operation amount of the flow control valve to produce in the first signal passage a control pressure different from load pressure; and a second signal passage for leading the control pressure in the first signal passage to the hydraulic fluid supply source, the valve apparatus being featured in further comprising a third signal passage for connecting the first signal passage to the upstream side of the first variable restrictor at a point between the check valve and the second variable restrictor, and a restrictor disposed in the third signal passage.
With that valve apparatus, the pressure upstream of the first variable restrictor is reduced by the restrictor in the third signal passage and then led to the first signal passage. Thus, the reduced pressure is led as the control pressure to the hydraulic fluid supply source to perform the load sensing control, so that the pump delivery pressure may be controlled not depending on the load pressure. Also, by adjusting respective openings of the restrictor in the first signal passage, the restrictor in the second signal passage, and the restrictor in the third signal pas
REFERENCES:
patent: 3856436 (1974-12-01), Lonnemo
patent: 4167893 (1979-09-01), Johnson
patent: 4336687 (1982-06-01), Morgan
patent: 4428400 (1984-01-01), Tantardini
patent: 4457341 (1984-07-01), Aspinwall
patent: 4515181 (1985-05-01), Dezelan
patent: 4617798 (1986-10-01), Krusche et al.
patent: 4738279 (1988-04-01), Kropp
patent: 4781219 (1988-11-01), Haarstad et al.
patent: 4914913 (1990-04-01), Germain et al.
patent: 4981159 (1991-01-01), Christensen et al.
patent: 5025625 (1991-06-01), Morikawa
patent: 5038671 (1991-08-01), Ueno
Hirata Toichi
Kajita Yusuke
Sugiyama Genroku
Hitachi Construction Machinery Co. Ltd.
Smith Leonard E.
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