Power plants – Pressure fluid source and motor – Having plural energy outputs
Patent
1990-07-09
1995-12-05
Look, Edward K.
Power plants
Pressure fluid source and motor
Having plural energy outputs
13759613, F16D 3102
Patent
active
054718392
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to valve apparatuses for use in hydraulic drive systems and, more particularly, to a valve apparatus having a plurality of directional control valves of closed center type arranged collectively and a hydraulic drive system having incorporated therein the valve apparatus, which are suitable for use in a working machine such as a construction machine, an industrial machine or the like in which a plurality of working elements are hydraulically driven.
BACKGROUND ART
As a representative example of a working machine in which a plurality of working elements are hydraulically driven, there are construction machines such as a hydraulic excavator, a hydraulic crane and so on. Each of these construction machines is equipped with a hydraulic drive system which is provided with a plurality of actuators for driving the plurality of working elements. In the hydraulic drive system, driving of the plurality of actuators is controlled by a plurality of directional control valves for controlling flows of hydraulic fluid delivered from a hydraulic pump.
By the way, as the hydraulic drive system of this kind, there is a system called a load sensing system in which, as disclosed, for example, in JP,A,60-11706, a pump delivery flow rate is controlled such that a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure of a plurality of actuators (a load pressure of a corresponding actuator in the case of individual operation) is retained to a prescribed value, so that the flow rate required for driving the actuators is delivered from the hydraulic pump. In the load sensing system, it is preferable to use a directional control valve of closed center type in which the spool closes the respective ports at a neutral position to prevent flow of the hydraulic fluid. Thus, unnecessary discharge of hydraulic fluid at the time each directional control valve is in the neutral position is minimized so that unloading operation of the hydraulic pump is made possible in combination with an unloading valve.
On the other hand, the plurality of directional control valves used in the hydraulic drive system are, in practice, formed as a valve apparatus in which the directional control valves are arranged collectively. The conventional valve apparatus having the directional control valves of closed center type are known from, for example, see JP,A,49-19282 and JP,A,54-59575. The conventional valve apparatus comprises a casing formed therein with a plurality of parallel spool bores arranged in a single row, a single common pump port, at least one tank port and a plurality of actuator ports with each pair associated with a single spool bore, and a plurality of spools slidably inserted respectively in the spool bores in the casing. The spools form respectively a plurality of directional control valves of closed center type, and each spool controls communication between the common pump port and tank port and the corresponding pair of the actuator ports. The common pump port communicates with a common pump line which extends perpendicularly to the plurality of parallel spool bores arranged in the single row, and successively passes through the spool bores.
However, the above-described conventional valve apparatus has the following problems.
The conventional valve apparatus is arranged such that the common pump line extends perpendicularly to the plurality of parallel spool bores arranged in the single row, and successively passes through the spool bores. For this reason, when the hydraulic fluid flows into the spools in the bores through the pump line, the hydraulic fluid surely passes through narrow grooves around one or more spools located upstream of the spool remotest from the pump port. Accordingly, pressure losses are large and cause an energy loss. Further, since temperature is raised due to an increase In heat generation, the reliability of the valve apparatus is deteriorated.
Furthermore, since the pressure losses are caused due to a passing of the hyd
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Hirata Toichi
Sugiyama Genroku
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Nguyen Hoang
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