HYDRAULIC CIRCUIT DEVICE OF CONSTRUCTION VEHICLE

Abstract: PCT No. PCT/JP89/00496 Sec. 371 Date Mar. 14, 1990 Sec. 102(e) Date Mar. 14, 1990 PCT Filed May 16, 1989 PCT Pub. No. WO89/11411 PCT Pub. Date Nov. 30, 1989.A hydraulic circuit apparatus for use in construction vehicles which is arranged to reduce pressure losses that occur when all the implement operating valves are kept at their neutral positions, to reduce the power consumption by all hydraulic pumps when the hydraulic circuit for implements require only a small amount of pressurized fluid, and to transmit a command signal to unload the surplus pressurized fluid when occasion demands. The circuit comprises a surplus pressurized fluid control circuit (50) to facilitate the regulation of changes in the fluid flow rate when changing over valves. The surplus pressurized fluid control circuit (50) has a pilot actuated type unloading valve (11) provided in a surplus pressurized fluid supply conduit (51) which is connected through a check valve 20 to a hydraulic pump (P1). The hydraulic pump (P1) is for the exclusive use of the implement. The conduit (51) is also connected to a drain conduit (Ct). A pilot pressure change-over valve (12) is provided in a pilot conduit (19) for the unloading valve (11).

Description: TECHNICAL FIELD OF THE INVENTION This invention relates to a hydraulic circuit apparatus for use in construction vehicles provided with a hydraulic circuit for power steering and a hydraulic circuit for implements and, more particularly, to a hydraulic circuit apparatus for construction vehicles arranged such that pressurized fluid in an amount more than that required for power steering is allowed to join the fluid flow to be supplied into the hydraulic circuit for implements thereby increasing the operating speed of the implements according to the preamble of claim 1. BACKGROUND ART OF THE INVENTION One embodiment of prior art hydraulic circuit apparatus for use in construction vehicles is shown in Fig. 1. As shown in the drawing, this hydraulic circuit apparatus comprises a plurality of hydraulic pumps P 1 , P 2 and P 3 for supplying fluid under pressure, and a flow control valve 6 which serves to allow the pressurized fluid in an amount more than that required for a hydraulic circuit 5 for power steering to join the fluid flow through a hydraulic circuit A for implements. Reference characters c and d denote valves for operating the implements, adapted for controlling the supply of fluid under pressure to hydraulic cylinders 22 and 23 for actuating the implements. Reference character e denotes a main relief valve, and T a fluid tank or reservoir. To improve the maneuverability of the implements in the above-mentioned prior art hydraulic circuit apparatus shown in Fig. 1, there is a conventional hydraulic circuit B for implements as shown in Fig. 2, which comprises, in addition to the hydraulic circuit A for implements shown in Fig. 1, implement operating valves 7 and 8 and pressure compensating flow control valves 9 and 10 associated, respectively, therewith. In Fig. 2, reference numerals 9' and 10' indicate springs, and 15, 16, 17 and 18 pilot pipings. Further, in case the hydraulic circuit for implements is kept at a high pressure and large quantities of fluid under pressure is not required for the hydraulic circuit for implements, there is used a prior art arrangement as shown in Fig. 3 wherein an unloading valve c is used to unload the pressurized fluid in an amount more than that required for the hydraulic circuit 5 for power steering upstream of the hydraulic circuit for implements A and B thereby reducing the power consumption for the latter. In case the above-mentioned prior techniques are used, there are problems as follows. (1) In case the pressure compensating flow control valves 9 and 10 are additionally provided as shown in Fig. 2, when the hydraulic circuit for implements is at its neutral position (stating more specifically, the implement operating valves 7 and 8 assume their positions 7 2 and 8 2 , respectively), it is required to provide a fluid actuating pressure which can overcome the resilient forces of the springs 9' and 10' in the pressure compensating flow control valves 9 and 10, respectively, (This fluid pressure is produced in the pilot pipings 15, 17) thus causing pressure losses corresponding to the fluid actuating pressure. (2) In the above-mentioned prior art hydraulic circuit apparatuses shown in Figs. 1 and 2, in case the flow rate of fluid under pressure delivered by the hydraulic pump P 1 suffices the requirements of the hydraulic circuit A or B for implements, the fluid under pressure in an amount or a flow rate more than that to be supplied into the hydraulic circuit 5 for power steering becomes useless, and the fluid pressure for the hydraulic circuit for implements is loaded on the hydraulic pump P 2 or P 3 , thus causing a high power consumption for the latter. (3) In the above-mentioned prior art hydraulic circuit apparatuses shown in Figs. 1, 2 and 3, because of a high rate of fluid flow through the implement operating valves (c, d in Fig. 1, and 7, 8 in Fig. 3), there is a tendency of causing a rise in fluid temperature and generating noise due to the fluid pressure. The document FR-A-24 18 358 relates to a hydraulic circuit according to the preamble of claim 1 and discloses an unloading valve, but the complete hydraulic circuit for opening a relief conduit for a pump is not controlled by the pressure generated of the pump itself which is to be controlled, but is connected via a pilot conduit with a command conduit. The command conduit can be linked to any pressure source. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances in the prior art, and has for its object to provide a hydraulic circuit apparatus for use in construction vehicles wherein when a plurality of implement operating valves are all kept at their neutral positions the fluid under pressure in an amount more than that required for a hydraulic circuit for power steering is not allowed to flow into a hydraulic circuit for implements so as to enable power losses at the neutral positions of the valves to be reduced. Another object of the present invention is to provide a hydraulic circuit apparatus for use in construction vehicles wherein when the hydraulic circuit for implements requires only a small amount of fluid under pressure only the fluid under pressure deliverred by one hydraulic pump out of the plurality of pumps is allowed to be supplied into the hydraulic circuit for implements so as to enable power consumption by all the hydraulic pumps to be reduced. A further object of the present invention is to provide a hydraulic circuit apparatus for use in construction wherein when the fluid under pressure in an amount more than that required to be supplied into the hydraulic circuit for sterring is unloaded when the hydraulic circuit for implements is kept at a high pressure an unloading command can be selected freely, and changes in the flow rate of fluid under pressure which occur when changing over the unloading valve can be regulated readily. The objects of the invention are achieved by a hydraulic circuit apparatus for construction vehicles according to the characterizing features of claim 1. circuit for work implements, and a pilot actuated type unloading valve adapted to control the flow rate of the fluid under pressure at the time when the remainder of fluid under pressure to be supplied into the hydraulic circuit for power steering is supplied into the hydraulic circuit for implements. According to a further aspect of the present invention, there is provided a hydraulic circuit apparatus for use in construction vehicles as set forth in the first aspect, characterized in that a pilot pressure change-over valve is provided in a pilot piping connected to the pilot actuated type unloading valve adapted to control the flow rate of the fluid under pressure at the time when the remainder of fluid under pressure to be supplied into the hydraulic circuit for power steering is supplied into the hydraulic circuit for implements so that the hydraulic pressure within the pilot piping is changed over so as to unload the pilot actuated type unloading valve when the hydraulic pressure within the pilot piping exceeds a preset value. Preferred embodiments are disclosed in the further sub-claims. The present invention has the following advantages. (1) Since when all the implement operating valves are kept at their neutral positions the surplus fluid under pressure in the hydraulic circuit for power steering is not allowed to flow into the hydraulic circuit for implements, the fluid flow through the implement operating valves is reduced to thereby enable pressure losses at the neutral position to be reduced. (2) Since when the hydraulic circuit for implements requries only a small amount of fluid under pressure only the pressurized fluid deliverred by one hydraulic pump out of the plurality of pumps is supplied, the power consumption by the hydraulic pumps can be reduced. (3) Since in case the surplus fluid under pressure in the hydraulic circuit for power steering is unloaded when the hydraulic circuit for implements is kept at a high pressure the change-over of the pilot actuated type unloading valve is performed by means of the pilot pressure change-over valve, an unloading command can be selected freely, and changes in the flow rate of fluid under pressure which occur when changing over the unloading valve can be regulated freely. The above-mentioned objects, aspects and advantages of the present invention will become apparent to those skilled in the art by making reference to the following detailed description and the accompanying drawings in which preferred embodiments incorporating the principles of the present invention are shown by way of examples only. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1, 2 and 3 are schematic explanatory views showing the constructions of prior art hydraulic circuit apparatuses for use in construction vehicles; Fig. 4 is a schematic explanatory view showing the construction of one embodiment of the present invention; Fig. 5 is a table which summarizes operating conditions of the embodiment shown in Fig. 1; and Fig. 6 is a schematic, constructional explanatory view showing principle parts of another embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will now be described below by way of examples only with reference to Figs. 4 to 6. In these drawings, the component parts having the same functions as those of the component parts of the prior art hydraulic circuit apparatuses shown in Figs. 1 to 3 are indicated with the same reference numerals, and further description of them is omitted herein to avoid duplication of explanation thereof. In Fig. 4 showing the first embodiment of the present invention, a hydraulic circuit 40 for implements comprises a first implement operating valve 7 and a second implement operating valve 8 which are provided with a first pressure compensating flow control valve 9 and a second pressure compensating flow control valve 10, respectively. The arrangement is made such that the pressure compensating flow control valves 9 and 10 supply fluid under pressure into the implement operating valves 7 and 8, respectively, in accordance with the manipulated variable of the valves 7 and 8, respectively, so that hydraulic cylinders 22 and 23 for driving implements can be controlled by the implement operating valves 7 and 8, respectively. The first pressure compensating flow control valve 9 is arranged to be changed from its unloading position 9a over to its loading position 9b under the action of a differential pressure between the pressure downstream of the first pressure compensating flow control valve 9 led by way of a pilot conduit 15 and the pressure downstream of the first implement operating valve 7 led by a third pilot conduit 16. Further, the second pressure compensating flow control valve 10 is arranged to be changed in the same manner from its unloading position 10a over to its loading position 10b under the action of a differential pressure between the pressure downstream of the second pressure compensating flow control valve 10 led by way of a pilot conduit 17 and the pressure downstream of the implement operating valve 8 led by way of a fourth pilot conduit 18. Reference character P 1 denotes a first hydraulic pump for supplying fluid under pressure for exclusive use by the implements. The fluid under pressure deliverred by the hydraulic pump P 1 is supplied by way of a first supply conduit 1 into a hydraulic circuit 40 for implements. Further, reference characters P 2 and P 3 denote a second hydraulic pump and a third hydraulic pump for supplying fluid under pressure through a flow control valve 6 and a second supply conduit 2 and a third supply conduit 3, respectively, into the hydraulic circuit 5 for power steering, and the hydraulic circuit 40 for implements. In the next place, a surplus pressurized fluid control circuit 50 will be described. The first and second pilot conduits 16 and 18 of the first and second pressure compensating flow control valves 9 and 10 for the first and second implement operating valves 7 and 8 are connected to load pressure chambers 22a and 23a, respectively, of the hydraulic cylinders 22 and 23 for driving implements. Further, a pilot actuated type unloading valve 11 is provided in a surplus pressurized fluid supply conduit 51 which is connected through a check valve 20 between the first supply conduit 1, which connects the hydraulic pump P 1 and the first pressure compensating flow control valve 9, and a drain conduit Ct. This pilot actuated type unloading valve 11 serves to either allow the surplus pressurized fluid from the above-mentioned second and third hydraulic pumps P 2 and P 3 to flow through the flow control valve 6 and the second supply conduit 2 into the hydraulic circuit 40 for implements, or unload the surplus fluid into the drain conduit Ct. The check valve 20 is connected to the surplus pressurized fluid conduit 51 connected between the first and second supply conduits 1 and 2. The above-mentioned pilot actuated type unloading valve 11 is subjected at its both ends the pressure downstream of the check valve 20 which is led by a third pilot conduit 21 and the pressures within the first and second pilot conduits 16 and 18 of the first and second pressure compensating flow control valves 9 and 10, respectively, which are led through a shuttle valve 13 and a fourth pilot conduit 19. This fourth pilot conduit 19 is provided with a pilot pressure change-over valve 12. A pilot pressure drainage conduit 52 is connected through a pilot relief valve 14 between the above-mentioned shuttle valve 13 and the drain conduit Ct. The operation of the hydraulic circuit apparatus of the present invention having the above-mentioned arrangement will be described below. (1) When both the implement operating valves 7 and 8 are located at their neutral positions 7n and 8n, respectively, as shown in Fig. 4: The pressure compensating flow control valves 9 and 10 assume their unloading positions 9a and 10a, respectively, since their springs 9' and 10' are pushed by the pilot fluid pressure delivered by the first hydraulic pump P 1 through the pilot conduits 15 and 17, respectively. In the same manner as the pressure compensating flow control valves 9 and 10, the pilot actuated type unloading valve 11 also assumes its unloading position. (as shown in Fig. 4) Thus, since the pressure for actuating the pressure compensating flow control valves 9 and 10 and the pilot actuated type unloading valve 11 is determined by the amount of pressurized fluid discharged by the pump P 1 and kept at a low value, pressure losses are small. (2) When the amount of the fluid discharged by the first hydraulic pump P 1 is sufficient to cover the total flow rate of the fluid under pressure required by the implement operating valves 7 and 8: The pressure compensating flow control valves 9 and 10 associated with the implement operating valves 7 and 8 manipulated by the operator act to allow the fluid under pressure discharged by the hydraulic pump P 1 to flow partially into the hydraulic circuit 40 for implements at a flow rate required by the implement operating valves 7 and 8. At that time, the differential pressure between the pressure downstream of the implement operating valves 7 and 8 led by the first pilot conduit 19 and the pressure in the second pilot 21 has not yet dropped to such a value as to allow extension of a spring 11' mounted in the unloading valve 11. Therefore, the pilot actuated type unloading valve remains unloading the surplus fluid under pressure from the second and third hydraulic pumps P 2 and P 3 . As a result, only the pressure discharged by the hydraulic pump P 1 is loaded in the hydraulic circuit 40 for implements so that the power consumption by the hydraulic pump is kept low. (3) When the amount of the fluid discharged by the first hydraulic pump P 1 is insufficient to cover the total flow rate of the fluid under pressure required by the implement operating valves 7 and 8: The differential pressure between the pressure in the second pilot conduit 21 and that in the first pilot conduit 19 becomes lower than the resilient force of the spring 11'. As a result, the pilot actuated type unloading valve 11 is shut off so as to allow the surplus pressurized fluid from the hydraulic pumps P 2 and P 3 , which is originally to be supplied into the hydraulic circuit 5 for power steering, to flow into the hydraulic circuit 40 for implements by a flow rate which corresponds to the shortage in the amount of the fluid discharged by the hydraulic pump P 1 . In consequence, the pressure in the hydraulic circuit 40 for implements is increased, and in case the fluid pressure in the pilot pressure drainage conduit 52 overcomes the resilient force of a spring 12' mounted in the pilot pressure change-over valve 12, the latter is changed from its loading position 12a as shown over to its unloading position 12b thereby shutting off the pilot fluid under pressure from the first pilot conduit 19 and draining the pressurized fluid in the chamber of the unloading valve 11 in which the spring 11' is mounted into the fluid tank or reservoir T. As a result, the spring 11' of the pilot actuated type unloading valve 11 is urged or compressed by the pressure prevailing in the second pilot conduit 21 so as to drain or unload all the surplus fluid under pressure supplied through the second supply conduit 2 by the second and third hydraulic pumps P 2 and P 3 into the fluid tank T. Accordingly, when the hydraulic circuit 40 for implements is kept at a high pressure, only the pressure discharged by the first hydraulic pump P 1 is loaded in the hydraulic circuit 40 for implements regardless of the amount of manipulation or the manipulated variable of the implement operating valves 7 and 8, and therefore the power consumption by the pumps is kept low. As is obvious from the foregoing description, the surplus pressurized fluid control circuit 50 forms the main point of the hydraulic circuit apparatus of the present invention. Further, reference numerals 7a and 8a denotes operative positions of the implement operating valves 7 and 8, respectively, and 7b and 8b returning or inoperative positions thereof. The above-mentioned operating conditions in Fig. 4 is summarized in Fig. 5. Fig. 6 is another embodiment of the present invention wherein the surplus pressurized fluid control circuit 50 and the pilot pressure change-over valve 12 shown in Fig. 4 are replaced with a solenoid actuated type surplus pressurized fluid control circuit 60 and a solenoid actuated type pilot pressure change-over valve 62, respectively. Reference numeral 64 denotes a detector adapted to detect input data on conditions (such as, for example, the fluid pressure in the hydraulic circuit 40 for implements shown in Fig. 4) for changing the pilot actuated type unloading valve 11 from its loading position over to its unloading position 62b, and 65 a controller adapted to output a signal for changing over the detector 64. These detectors are not shown in Fig. 4.

Claims: A hydraulic circuit apparatus for use in construction vehicles comprising a hydraulic circuit for power steering (5) to which a fluid under pressure is supplied from a second hydraulic pumping means (P 3 ), a hydraulic circuit (40) for work implements having at least two hydraulic actuators (22,23) driven by a plurality of implement operating valves (7,8) respectively, and being connected to a first hydraulic pumping means (P 1 ) through a first supply conduit (1) to receive a fluid under pressure from the first hydraulic pumping means (P 1 ), and to the drain conduit, the arrangement being such that the fluid under pressure in an amount more than that required to be supplied into the hydraulic circuit for power steering (5) is allowed to join the fluid to be supplied into hydraulic circuit for implements (40), wherein said hydraulic circuit apparatus comprises a plurality of pressure compensating flow control valves (9,10) adapted to control the flow rate of the fluid under pressure to be supplied into the plurality of implement operating valves (7n,8n) respectively, and wherein a pilot actuated type unloading valve (11) is placed on the way of a third supply conduit (51) connecting a second supply conduit (2) and a drain conduit (Ct), a check valve (20) connecting the first and second supply conduits (1,2), characterized by a surplus pressurized fluid control circuit (50) adapted to control the flow rate of the fluid under pressure at the time when the ramainder of fluid under pressure to be supplied into the hydraulic circuit for power steering (5) is supplied into the hydraulic circuit for work implements (40), wherein the surplus pressurized fluid control circuit (50) comprises the pilot actuated type unloading valve (11) whereas pressure downstream of the plurality of implement operating valves and supply pressure in the supply conduit being applied as pilot pressure through a first (19) and a second (21) pilot conduit, respectively, a change-over valve (12) placed in the first pilot conduit (19) and changed over to the drain conduit (Ct) so as to unload the unloading valve (11) when the hydraulic pressure within the first pilot conduit (19) exceeds a preset value, and a pilot relief valve (14) connected between the first pilot conduit (19) and the drain conduit (Ct). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 1, wherein said change-over valve (12) is a pilot pressure change-over valve placed in the first pilot conduit (19), the pressure downstream of the plurality of implement operating valves (7,8) being applied as pilot pressure through a pilot pressure drainage conduit (52). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 2, wherein said preset value is determined by a resilient force of a spring (12') of the pilot pressure change-over valve (12). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 1, wherein said change-over valve is a solenoid actuated type pilot pressure change-over valve (62) placed in the first pilot conduit (19). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 1, wherein said pilot actuated type unloading valve (11) has a mechanism of comparing a difference in the two pilot pressures through the first (19) and second (21) pilot conduits with a resilient force of a spring (11') of the pilot actuated type unloading valve (11). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 1, wherein a check valve (20) is placed in an upstream region of the third supply conduit (51). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 1, wherein a shuttle valve (13) is placed in said first pilot conduit (19), the shuttle valve being connected to each of said plurality of implement operating valves (7,8). A hydraulic circuit apparatus for use in construction vehicles as claimed in claim 1, wherein said second hydraulic pumping means consists of two hydraulic pumps (P 2 ,P 3 ).

Inventors: IKARI MASANORI, IKARI, MASANORI
Applicants: KOMATSU MEC CORP, KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO, KOMATSU MEC CORPORATION
Application year: 1989
Main classification: B62D5
IPC codes: F15B11, E02F9, B62D5