PRESSURE OIL FEED CIRCUIT DEVICE FOR HYDRAULIC CYLINDER OF OPERATION MACHINE

Abstract: This invention intends to provide a pressure oil feed circuit device for a hydraulic cylinder of an operation machine which can control a pump discharge flow rate so that the difference between a pump discharge pressure and a load pressure becomes constant during the normal operation of the operation machine and can control the discharge flow rate of the pump so to decrease it during the fine operation of the operation machine. The pressure oil feed circuit device includes a larger diameter piston (9) for operating the capacity regulation member (8) of a variable capacity pump (2) in such a direction as to reduce the pump capacity; a smaller diameter piston (10) for operating the capacity regulation member (8) of the variable capacity pump (2) in such a direction as to increase the pump capacity, the smaller diameter piston (10) having a small diameter piston pressure receiving chamber (10a) connected to the pump discharge passage (2a); a load sensing valve (11) for establishing/cutting off communication between the pressure receiving chamber (9a) of the larger diameter piston and the pump discharge passage; and means (12, 13, 14) for providing the load sensing valve with a push force exerted in the direction of establishing communication between the pump discharge passage (2a) and the larger diameter piston pressure receiving chamber (9a).

Description: TECHNICAL FIELD OF THE INVENTION This invention relates to a hydraulic circuit apparatus for supplying fluid under pressure discharged by a hydraulic pump into hydraulic cylinders for actuating a work implement of a construction vehicle such as a power shovel or the like. BACKGROUND ART OF THE INVENTION A hydraulic circuit apparatus arranged so as to supply fluid under pressure discharged by a hydraulic pump into hydraulic cylinders for a work implement through operating valves is heretofore well known. In case of conducting earth scraping-off operation and slope correcting operation by a power shovel, it is necessary to perform inching operation of the work implement of the power shovel. This inching operation of the work implement is achieved by supplying extremely small amounts of fluid under pressure discharged by a hydraulic pump into hydraulic cylinders for the work implement. However, it is quite difficult to control finely the amount of fluid under pressure to be supplied into the hydraulic cylinders for the work implement and it is also quite difficult to inch the work implement as desired. As a result the operational accuracy in earth scapping-off operation and slope correcting operation becomes low. One solution to overcome the problems involved in inching operation is given in EP-A-0 349 092, which application was published after the priority date of the present application. In EP-A-0 349 092 a hydraulic drive system is disclosed which may be operated in a normal mode and in a fine operation mode. In the normal mode the discharge rate of a hydraulic pump is controlled to hold a differential pressure between a discharged pressure of the hydraulic pump and a load pressure of an actuator at a setting value. In the fine operation mode the flow rate supplied to the actuator at the same stroke of a control lever as that in the ordinary work is reduced to facilitate operation of the actuator at a finely adjusted speed for permitting fine operation with ease. According to one embodiment of EP-A-0 349 092 an instruction unit is only operated when the fine operation mode should be obtained. The instruction unit is connected to a controller which operates a control force supplying device so arranged to apply a control force of a plunger to one end of a control valve. The control valve is a part of the load-sensing control device and further comprises a drive part on the same side as the plunger and another drive part and spring on the side opposite to the plunger. The control valve is used to connect a large-diameter pressure receiving portion of a regulator with a tank, with a discharge line of the pump or to connect this portion with both the tank and the discharge line at a ratio corresponding to the position of the control valve. Further, the regulator comprises a small-diameter pressure receiving portion connected to the discharge line of the pump. The regulator is used for changing a swash plate of the pump and to thereby control the discharge rate of the pump and to hold the differential pressure at a setting value. SUMMARY OF THE INVENTION The present invention has for its object to provide a hydraulic circuit apparatus for supplying fluid under pressure into hydraulic cylinders for a work implement whereby stable operation of the working implement is also ensured during inching operation whereby the number of parts of the apparatus is decreased and the costs of manufacturing the apparatus is reduced. To achieve the above-mentioned object a hydraulic circuit apparatus according to claims 1 or 3 is provided. Further features for advantageous embodiments of the invention are disclosed by the subclaims. According to the present invention incorporating the above-mentioned aspects, since the flow rate of fluid discharged by the variable displacement pump is controlled in such a manner that the difference between the discharge pressure of the pump and the load pressure is always kept constant, a stable operation of the work implement is ensured, and also during inching operation of the work implement the displacement regulating member of the variable displacement member of the variable displacement pump can be actuated in such a direction as to reduce the displacement of the pump by applying pushing forces to the load sensing valve so as to push its spool in such a direction as to communicate the discharge passage of the pump with the pressure receiving chamber of the large diameter piston. Accordingly, since during inching operation of the work implement the flow rate of fluid discharged by the variable displacement pump can be reduced, the amount of fluid under pressure to be supplied into the hydraulic cylinders for the work implement can be controlled finely to an extremely small amount so that the inching operational characteristic can be enhanced. The above-mentioned and other objects, aspects and advantages of the present invention will become apparent to those skilled in the art when reference is made to the following description and the accompanying drawings in which preferred embodiments incorporating the principles of the present invention are shown by way of example only. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a hydraulic circuit diagram showing a first embodiment of the present invention; Fig. 2 is a graph showing the relationship between the flow rate of fluid under pressure supplied into hydraulic cylinders for a work implement and the stroke of an operating valve associated therewith; and Fig. 3 is a hydraulic circuit diagram showing a second embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will now be described in detail below by way of several preferred embodiments thereof with reference to the accompanying drawings. Referring first to Figs. 1 and 2, the first embodiment of the present invention is described. A variable displacement pump 2 driven by an engine 1 has a discharge passage 2a connected with inlets of a plurality of operating valves 3, whose outlet sides are connected by their respective conduits 4 with hydraulic cylinders 5 of work implements, respectively. Each conduit 4 is provided with a pressure compensating valve 6. The load pressures P LS in the conduits 4 are compared by a shuttle valve 7, and a higher load pressure P LS detected as a result of the comparison is introduced into spring chambers of the pressure compensating valves 6 so that the valves 6 may be set at a pressure corresponding to the higher load pressure P LS . By so doing, the fluid under pressure discharged by one variable displacement pump 2 can be supplied to the hydraulic cylinders 5 for work implement. The displacement of fluid from the variable displacement pump 2 is controlled so that the difference between the discharge pressure P 1 and the load pressure P LS is always kept constant. Stating more specifically, a displacement regulating member 8 of the variable displacement pump 2 is actuated by a large piston 9 in such a direction as to reduce the displacement, and by a small piston 10 in such a direction as to increase the displacement. Further, a pressure receiving chamber 9a of the large piston 9 is controlled to be selectively connected through a load sensing valve 11 either with a fluid tank or with the discharge passage 2a, and a pressure receiving chamber 10a of the small piston 10 is connected with the discharge passage 2a. The above-mentioned load sensing valve 11 has a spool arranged to be pushed by the pressure in the discharge passage 2a; that is, the discharge pressure P 1 and the thrust created by a proportional position action electromagnetic solenoid 12 in such a direction as to incresed the area of its port communicating with the pressure receiving chamber 9a of the large piston 9, and also pushed by the outlet pressure in the operating valves 3; that is, the load pressure P LS in such a direction as to reduce the area of the port thereof communicating with the pressure receiving chamber 9a. This load sensing valve 11 is arranged to effect control such that where the thrust created by the proportional position action electromagnetic solenoid 12 is zero, and when the difference between the discharge pressure P 1 and the load pressure P LS (P 1 - P LS ) is increased, the pressure in the pressure receiving chamber 9a of the large piston 9 is increased so as to actuate the displacement regulating member 8 in such a direction as to reduce the displacement to thereby reduce the discharge flow rate per one revolution to reduce the discharge pressure P 1 . Whilst, where the thrust created by the solenoid 12 is zero, and when the difference between the discharge pressure P 1 and the load pressure P LS (P 1 - P LS ) is reduced, the pressure in the pressure receiving chamber 9a of the large piston 9 is reduced so as to actuate the displacement regulating member 8 in such a direction as to increase the displacement to thereby increase the discharge flow rate per one revolution to incresae the discharge pressure P 1 , whereby controlling the displacement of fluid from the variable displacement pump 2 so that the difference between the discharge pressure P 1 and the load pressure P LS (P 1 - P LS ) may always be kept constant. Further, when a thrust is created by the proportion position action electromagnetic solenoid 12, the spool of the load sensing valve 11 is pushed in such a direction as to increase the area of the port thereof communicating with the pressure receiving chamber 9a so as to increase the pressure in the chamber 9a of the large piston 9 regardless of the pressure between the discharge pressure P 1 and the load pressure P LS to move the displacement regulating member 8 in a direction to reduce the displacement, thereby reducing the flow rate of fluid per one revolution. Stating in brief, the pressure difference between the discharge pressure P 1 and the load pressure P LS is reduced by the thrust created by the proportional position action solenoid 12 so as to reduce the discharge flow rate of fluid from the variable displacement pump 12. The above-mentioned proportional position action electromagnetic solenoid 12 is supplied with electric current from a controller 13, to which a mode signal from a mode change-over switch 14 is inputted. When a normal mode signal is inputted by the mode change-over switch 14 to the controller 13, the proportional position action electromagnetic solenoid 12 is not supplied with electric current, whilst when an inching operation mode signal is inputted by the mode change-over switch 14 to the controller 13, the electromagnetic solenoid 12 is supplied with electric current. Such being the arrangement, during inching of the work implement, the flow rate of fluid discharged by the variable displacement pump 2 becomes less than that in the normal operation, so that the flow rate of fluid to be supplied into the hydraulic cylinders 5 for work implement changes in proportion to the stroke of the operating valves 3 as shown by a dotted line "A" in Fig. 2 and becomes less than the flow rate of fluid in the normal operation as shown by a solid line B in Fig. 2, thus rendering it possible to effect fine control of the amount of fluid supplied into the hydraulic cylinders 5 for the work implement to improve the inching operation characteristic. Fig. 3 shows the second embodiment of the present invention. In this embodiment, a pilot pump 15 is driven by an engine 1, and a discharge passage 15a of the pump 15 is connected through a change-over valve 16 with a pressure receiving section 11a of a load sensing valve 11. The change-over valve 16 is arranged to be kept at its shut-off position I by the resilient force of a spring mounted therein, and also kept at its communicating position II when its solenoid 16 is energized. The solenoid 16 is supplied with electric current from a power supply through a mode change-over switch 14 and the controller 13. Further, the component parts shown in Fig. 3 with the same reference numerals as those used in the first embodiment shown in Fig. 1 are the same component parts, and therefore description of them is omitted herein to avoid duplication of explanation. In the second embodiment shown in Fig. 3, when a mode change-over switch 14 is located at its inching operation mode position so as to input an inching operation mode signal from the switch 14 to a controller 13 and send an electric current to a solenoid 16a, thereby energizing the same, a change-over valve 16 is changed over to its communicating position II so that the pilot fluid under pressure from a pilot pump 15 is supplied into a pressure receiving section 11a of a load sensing valve 11, and as a result, its spool is pushed in such a direction as to increase the area of the port thereof communicating with pressure receiving chamber 9a of a large piston 9, thereby reducing the amount of fluid discharged by a variable displacement pump 2.

Claims: A hydraulic circuit apparatus for supplying fluid under pressure into a plurality of hydraulic cylinders (5) for a work implement arranged so as to connect a discharge passage (2a) of a variable displacement pump (2) through operating valves (3) with the cylinders for the work implement, said apparatus comprising: a large diameter piston (9) for actuating a displacement regulating member (8) of said variable displacement pump (2) in such a direction as to reduce the displacement of the pump; a small diameter piston (10) having a pressure receiving chamber (10a) connected with said discharge passage (2a) of the pump and adapted to actuate the displacement regulating member (8) of said pump in such a direction as to increase the displacement of the pump (2); a load sensing valve (11) adapted to connect or disconnect a pressure receiving chamber (9a) of said large diameter piston (9) with or from the discharge passage (2a) of said pump (2); means (12, 13, 14) for applying pushing forces to the load sensing valve (11) so as to push its spool in such a direction as to communicate the discharge passage (2a) of said pump (2) with the pressure receiving chamber (9a) of said large diameter piston (9); pressure compensating valves (6) interposed between said hydraulic cylinders (5) for a work implement and said operating valves (3); and a shuttle valve (7) for comparing load pressures (P LS ) in the output conduits (4) of said pressure compensating valves (6) to introduce a higher load pressure into a pressure receiving section provided on one side of said load sensing valve (11), wherein during normal operation of the work implement the flow rate of fluid discharged by the pump (2) is controlled in such a manner that the difference between the discharge pressure (P 1 ) of the pump (2) and the load pressure (P LS ) is always kept constant, whilst during inching operation of the work implement the flow rate of the fluid discharged by the pump (2) is reduced. A hydraulic circuit apparatus according to claim 1, characterized in that said pushing force applying means (12, 13, 14) comprises: a proportional position action electromagnetic solenoid (12) provided on one side of said load sensing valve (11) ; a mode change-over switch (14) for the electromagnetic solenoid (12); and a controller (13) adapted to receive an inching operation mode signal transmitted by the mode change-over switch (14) and to send an electric current to said electromagnetic solenoid (12). A hydraulic circuit apparatus for supplying fluid under pressure into a plurality of hydraulic cylinders (5) for a work implement arranged so as to connect a discharge passage (2a) of a variable displacement pump (2) through operating valves (3) with the cylinders (5) for the work implement, said apparatus comprising: a large diameter piston (9) for actuating a displacement regulating member (8) of said variable displacement pump (2) in such a direction as to reduce the displacement of the pump; a small diameter piston (10) having a pressure receiving chamber (10a) connected with said discharge passage (2a) of the pump (2) and adapted to actuate the displacement regulating member (8) of said pump in such a direction as to increase the displacement of the pump; a load sensing valve (11) adapted to connect or disconnect a pressure receiving chamber (9a) of said large diameter piston (9) with or from the discharge passage (2a) of said pump (2); and a means (13, 14, 15, 16, 16a) for applying pushing forces to the load sensing valve (11) so as to push its spool in such a direction as to communicate the discharge passage (2a) of said pump (2) with the pressure receiving chamber (9a) of said large diameter piston (9), wherein during normal operation of the work implement a flow rate of fluid discharged by the pump (2) is controlled in such a manner that the difference between the discharge pressure (P1) of the pump (2) and load pressure (P LS ) is always kept constant, whilst during inching operation of the work implement the flow rate of fluid discharged by the pump (2) is reduced; and said pushing force applying means (13, 14, 15, 16, 16a) comprises: a pilot pump (15); a conduit (15a) for introducing pilot fluid under pressure discharged by the pilot pump (15) into a pressure receiving section (lla) provided on one side of said load sensing valve (11); a change-over valve (16) provided in the conduit (15a); a proportional position action electromagnetic solenoid (16a) provided on one side of the change-over valve (16); a mode change-over switch (14) for the electromagnetic solenoid (16a), and a controller (13) adapted to receive an inching operation mode signal transmitted by the mode change-over switch (14) and to send an electric current to said electromagnetic solenoid (16a). Hydraulic circuit apparatus according to claim 3, characterized in that pressure compensating valves (6) are interposed between said hydraulic cylinders (5) for a work implement and said operating valves (3) and a shuttle valve (7) is provided for comparing load pressures in the output conduits (4) of said pressure compensating valves (6) to introduce a higher load pressure into a pressure receiving section provided on one side of said load sensing valve (11).

Inventors: AKIYAMA TERUO, ISHIZAKI NAOKI, SHINOHARA SHIGERU, SHIRAI KIYOSHI, TAKIGUCHI TAKAHIDE, AKIYAMA, TERUO, ISHIZAKI, NAOKI, SHINOHARA, SHIGERU, SHIRAI, KIYOSHI, TAKIGUCHI, TAKAHIDE, AKIYAMA, TERUO KAWASAKI FACT. OF K.K.K. S., ISHIZAKI, NAOKI KAWASAKI FACT.OF K.K.K. S., SHINOHARA, SHIGERU KAWASAKI FACT.OF K.K.K. S., SHIRAI, Kiyoshi Kawasaki Fact. of K.K.K. S., TAKIGUCHI, TAKAHIDE KAWASAKI FACT.OF K.K.K. S.
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1990
Main classification: F15B11
IPC codes: F15B11, E02F9, F04B49