Hydraulic Control Valve for a Front Loader Having a Multi-Circuit for an Agricultural Tractor

Abstract

The present invention relates to a hydraulic operating valve having a multi-circuit applied to a front loader of an agricultural tractor, and aims to selectively implement series and parallel hydraulic circuits in a single valve structure and to stably maintain carryover hydraulic flow. To this end, the present invention comprises an inlet port and a return port, first and second spool bores, a plurality of operating ports, a valve groove, and an inlet passage, a supply passage, an operating passage, a return passage, and a transmission passage connecting them, which are integrally formed in the valve body, a spool movably installed in each spool bore, and a check valve, a carryover plug, a junction groove, and an end cover. Accordingly, the present invention can stably form a series hydraulic circuit that sequentially operates two driving cylinders, and can be converted to and expanded into a parallel hydraulic circuit by changing the position of the circuit switching junction and plug. Furthermore, even in a non-operating state, the flow of hydraulic fluid is not interrupted and can be continuously supplied to an external hydraulic control valve, thereby providing high efficiency and reliability in various working environments.

Description

Technology Field

[0001] The present invention relates to a hydraulic operating valve applied to a front loader of an agricultural tractor, and more specifically, to a hydraulic operating valve having a multi-circuit capable of selectively implementing series and parallel hydraulic circuits in a single valve structure and stably maintaining carryover hydraulic flow. Background Technology

[0002] Work vehicles such as agricultural tractors are equipped with a main hydraulic operating valve to operate implements such as front loaders. In addition, various auxiliary devices may be mounted on the work vehicle, and it is common to provide a separate sub-hydraulic operating valve to operate these auxiliary devices independently of the front loader.

[0003] Meanwhile, the front loader of an agricultural tractor is used in various working environments, such as for transporting soil, stones, and wood, as well as for snow removal and feed transport, and the hydraulic characteristics required vary depending on the working conditions.

[0004] In this regard, hydraulic operating valves are classified into parallel hydraulic circuits and series hydraulic circuits depending on the configuration of the hydraulic circuit. The parallel hydraulic circuit is suitable for tasks requiring high output while driving multiple implements simultaneously, while the series hydraulic circuit is suitable for tasks requiring fast response and operating speed at relatively low loads.

[0005] As a technology for simultaneously operating the front loader and auxiliary device as described above, a structure in which a sub-hydraulic operating valve is attached to the side of the hydraulic operating valve has been proposed, and such prior art literature discloses the invention of the applicant of the present invention, "Published Patent Application No. 10-2023-0005449, Title / Hydraulic operating valve for work implement."

[0006] The above prior art discloses a technology that includes a first operating valve for supplying oil to a driving cylinder equipped with a work device mounted on a work vehicle, and a second operating valve detachably connected to the first operating valve for supplying oil to a driving cylinder of an auxiliary device, thereby enabling the installation of a sub-hydraulic operating valve without additional changes to the flow path and optimizing the flow path connection structure between the valves.

[0007] However, although the hydraulic operating valve of the aforementioned prior art includes a main hydraulic operating valve and a sub hydraulic operating valve, it has a limitation in that the hydraulic circuit is configured only in a parallel manner.

[0008] Accordingly, although it is necessary to selectively apply parallel hydraulic circuits and series hydraulic circuits depending on the working environment, there is a problem in that users must replace the entire hydraulic operating valve or perform complex internal structural modifications.

[0009] In particular, since the hydraulic circuit cannot be quickly switched in response to changes in the working environment, problems arise such as reduced work efficiency and decreased convenience of equipment operation.

[0010] In addition, there is a problem in that maintenance costs increase and downtime is prolonged because separate device replacement or disassembly is required to switch hydraulic circuits. The problem to be solved

[0011] The present invention aims to solve the problems of conventional hydraulic operating valves being limited to parallel hydraulic circuits, which make it difficult to select a hydraulic circuit according to the working environment, and the problems of requiring replacement of the operating valve or complex internal structural changes to change the hydraulic circuit. The invention provides a multi-circuit front loader hydraulic operating valve for agricultural tractors that can selectively switch between a parallel hydraulic circuit and a series hydraulic circuit, allows circuit switching with only simple structural changes without replacing a separate valve, and enables efficient independent control of the front loader and auxiliary devices. means of solving the problem

[0012] To solve the above problem, a hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor according to the present invention includes a main hydraulic operating valve, and the main hydraulic operating valve is configured to form a series hydraulic circuit.

[0013] To this end, the main hydraulic operating valve comprises a valve body, an inlet port and a return port formed in the valve body, a first spool bore and a second spool bore formed penetrating between the inlet port and the return port, a plurality of operating ports corresponding to the spool bore, a first valve groove and a second valve groove formed above the first spool bore and the second spool bore, and an inlet passage, a supply passage, an operating passage, a return passage, and a transmission passage interconnecting the inlet port, the first spool bore, the second spool bore, and the operating port.

[0014] In addition, a first spool and a second spool are movably installed in the first spool bore and the second spool bore, respectively, and a check valve is installed in the first valve groove and the second valve groove, respectively, to form a series hydraulic circuit that sequentially operates a plurality of driving cylinders by sequentially transmitting the flow of hydraulic fluid.

[0016] Next, the present invention is configured such that a sub-hydraulic operating valve forms a parallel hydraulic circuit. To this end, a junction groove is formed in the valve body, and the sub-hydraulic operating valve is configured to be assembled to the side of the valve body by inserting a circuit switching junction in the forward direction into the junction groove and changing the installation position of the first plug.

[0017] The above-described circuit switching junction is formed to include a hydraulic fluid discharge path, a discharge path, an inlet path communicating therewith, and a plurality of inlet holes, and the first plug is configured to be screw-coupled between the second inlet path and the second transfer path to establish a hydraulic fluid flow path.

[0018] Accordingly, the hydraulic fluid passing through the first transmission path passes through the second check valve, and a portion of it is branched off through the second inlet path and supplied to the sub-hydraulic operating valve, while the remaining hydraulic fluid continues to be transmitted along the series hydraulic circuit of the main hydraulic operating valve, thereby forming a series hydraulic circuit of the main hydraulic operating valve and a parallel hydraulic circuit of the sub-hydraulic operating valve, so as to enable the independent driving of multiple driving cylinders.

[0020] Furthermore, the present invention is configured such that a main hydraulic operating valve and a sub hydraulic operating valve form a continuous series hydraulic circuit. To this end, a circuit switching junction is inserted in the reverse direction into the junction groove, and a second plug is additionally installed in addition to changing the installation position of the first plug.

[0021] At this time, the first plug is configured to block the branching inflow of hydraulic fluid through the second inflow path, and the second plug is configured to prevent hydraulic fluid passing through the second transfer path from being returned to the hydraulic tank through the return port.

[0022] Accordingly, hydraulic fluid delivered from the main hydraulic operating valve is sequentially supplied to the sub hydraulic operating valve, and the main hydraulic operating valve and the sub hydraulic operating valve form a continuous series hydraulic circuit, thereby configuring a complex hydraulic circuit in which hydraulic fluid is delivered in stages. Effects of the invention

[0023] The hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor according to the present invention has the following effects.

[0024] First, the main hydraulic operating valve can stably form a series hydraulic circuit that sequentially operates two driving cylinders through the spool bore and the fluid path structure connecting it, so sufficient operating force can be secured even during high-load operations.

[0025] In addition, a sub-hydraulic operating valve can be easily added by inserting a circuit switching junction into the junction home and changing the installation position of the plug; in this case, the sub-hydraulic operating valve is switched to a parallel hydraulic circuit and can independently drive a separate driving cylinder, thereby enabling various operating modes depending on the working environment.

[0026] Furthermore, through the combined structure of the circuit switching junction and junction groove described above, the main hydraulic operating valve and the sub hydraulic operating valve can be configured as a continuous series hydraulic circuit, enabling complex operations in which multiple driving cylinders are operated in stages.

[0027] In addition, by preventing backflow of hydraulic fluid through check valves, interference between circuits is minimized, and stable hydraulic control is possible.

[0028] In addition, the main hydraulic operating valve of the present invention prevents the leakage of unnecessary hydraulic fluid by means of a closing plug and a carryover plug, and can supply hydraulic fluid to an external hydraulic operating valve through a carryover path when necessary, thereby improving hydraulic efficiency.

[0029] In addition, the present invention can utilize the advantages of both parallel hydraulic circuits and series hydraulic circuits. That is, when a parallel hydraulic circuit is applied, multiple work members can be driven independently, thereby improving work responsiveness and simultaneous workability, and when a series hydraulic circuit is applied, the flow of hydraulic fluid is transmitted sequentially, thereby ensuring operational stability of the drive cylinder and circuit continuity.

[0030] In addition, even when the first spool, second spool, and third spool are in a non-operating state, hydraulic fluid can be continuously supplied from the main hydraulic operating valve through the sub hydraulic operating valve and then back through the main hydraulic operating valve to the external hydraulic operating valve; thus, even in a system where multiple hydraulic operating valves are connected in series or parallel, the flow of hydraulic fluid can be maintained stably without interruption.

[0031] Accordingly, the present invention can form a composite hydraulic circuit combining a series hydraulic circuit and a parallel hydraulic circuit, so that high-load work and fast repetitive work can be performed simultaneously in one system, and can flexibly respond to various agricultural and loader work environments.

[0032] Furthermore, due to the structure in which hydraulic fluid passes through a sub-hydraulic control valve, it is easy to connect additional hydraulic devices, and since the system can be expanded without changing the fluid path, the scope of application is expanded.

[0033] Finally, by maintaining a consistent hydraulic supply path through the carryover Euro, pressure loss is minimized and the efficiency and reliability of the entire hydraulic system can be improved. Additionally, since various circuit configurations are possible simply by changing the junction structure and plug position without replacing separate valves, the structure is simplified and operator convenience is enhanced. Brief explanation of the drawing

[0034] FIG. 1 is a perspective view of a main hydraulic operating valve to which the present invention is applied. FIG. 2 is an exploded perspective view of the main hydraulic operating valve of the present invention. FIG. 3 is a plan view of the main hydraulic operating valve of the present invention. FIG. 4 is a rear view of the valve body of the present invention. FIG. 5 is a plan cross-sectional view of the main hydraulic operating valve of the present invention. FIG. 6 is a cross-sectional view along line AA of FIG. 3 of the present invention. FIG. 7 is a front cross-sectional view of the valve body of the present invention. FIG. 8 is a cross-sectional view along line BB of FIG. 7 of the present invention. FIG. 9 is a front cross-sectional view of a valve body showing the first and second return passages of the present invention. FIG. 10 is a side cross-sectional view showing the first transmission channel of the present invention. FIG. 11 is a cross-sectional view along the CC line of FIG. 7 of the present invention. FIG. 12 is a hydraulic circuit diagram of the main hydraulic operating valve of the present invention. FIG. 13 is a perspective view of the assembled state of the main hydraulic operating valve and the sub hydraulic operating valve of the present invention. FIG. 14 is an exploded perspective view of a main hydraulic operating valve and a sub hydraulic operating valve for a parallel circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 15 is a perspective view of the assembled state of the main hydraulic operating valve and the sub hydraulic operating valve of the present invention. FIG. 16 is a plan cross-sectional view of a main hydraulic operating valve and a sub hydraulic operating valve for a parallel circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 17 is a perspective view of the circuit switching junction of the present invention. FIG. 18 is a plan cross-sectional view of the circuit switching junction of the present invention. FIG. 19 is an enlarged view of section "A" of FIG. 16 of the present invention. FIG. 20 is a cross-sectional view of a main hydraulic operating valve and a sub hydraulic operating valve for a parallel circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 21 is a hydraulic circuit diagram of a main hydraulic operating valve and a sub hydraulic operating valve for a parallel circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 22 is an exploded perspective view of a main hydraulic operating valve and a sub hydraulic operating valve for a series circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 23 is a plan cross-sectional view of a main hydraulic operating valve and a sub hydraulic operating valve for a series circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 24 is an enlarged view of section "B" of FIG. 23 of the present invention. FIG. 25 is a cross-sectional view of a main hydraulic operating valve and a sub hydraulic operating valve for a series circuit configuration of the sub hydraulic operating valve of the present invention. FIG. 26 is a hydraulic circuit diagram of a main hydraulic operating valve and a sub hydraulic operating valve for the series circuit configuration of the sub hydraulic operating valve of the present invention. Specific details for implementing the invention

[0035] We will now describe a preferred embodiment for more specifically implementing the means for solving the problem that the present invention aims to solve.

[0036] A hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor according to a preferred embodiment of the present invention is configured to include a main hydraulic operating valve (100).

[0037] The main hydraulic operating valve (100) is formed to form a series hydraulic circuit for sequentially operating two first and second driving cylinders (S1)(S2) mounted on the front loader of an agricultural tractor. To this end, the main hydraulic operating valve (100) includes a valve body (110), and the valve body (110) integrally forms an inlet port (111), a return port (112), a first spool bore (113), a second spool bore (114), first to fourth operating ports (115)(116)(117)(118), a first valve groove (119), a second valve groove (120), and a plurality of fluid passages connecting them.

[0038] The inlet port (111) is a part through which hydraulic fluid supplied from the hydraulic pump (1) flows into the valve body (110), and the return port (112) is a part through which hydraulic fluid that has finished operating is returned to the hydraulic tank (2). In this embodiment, the inlet port (111) and the return port (112) may each be formed on both sides of the lower rear of the valve body (110).

[0039] A first spool bore (113) and a second spool bore (114) are formed between the inlet port (111) and the return port (112), penetrating in the front-rear direction of the valve body (110). The first spool bore (113) and the second spool bore (114) are spaces into which the first spool (140) and the second spool (140a) are respectively slidably inserted, and are configured to selectively open, close, or switch the flow of hydraulic fluid.

[0040] A first spool (140) is movably installed in the first spool bore (113), and a second spool (140a) is movably installed in the second spool bore (114). The first spool (140) and the second spool (140a) are configured to control the operation of corresponding first and second drive cylinders (S1) and (S2), respectively. That is, the fluid path is selectively opened and closed so that hydraulic fluid is supplied to or returned to the operating port side depending on the moving position of the spool.

[0041] First to fourth operating ports (115)(116)(117)(118) are formed on the rear side of the valve body (110). Specifically, as shown in FIG. 4, a first operating port (115) and a third operating port (116) are formed on the upper side of the first spool bore (113) and the second spool bore (114), respectively, and a second operating port (117) and a fourth operating port (118) can be formed on the upper side of the inlet port (111) and the return port (112), respectively. Accordingly, the first operating port (115) and the second operating port (117) are connected to the first driving cylinder (S1), and the third operating port (116) and the fourth operating port (118) are connected to the second driving cylinder (S2), so that the two first and second driving cylinders (S1) and (S2) can be operated sequentially.

[0042] A first valve groove (119) and a second valve groove (120) are formed on the upper surface of the upper valve body (110) of the first spool bore (113) and the second spool bore (114), respectively. A first check valve (150) and a second check valve (150a) are installed in the first valve groove (119) and the second valve groove (120), respectively. The first check valve (150) and the second check valve (150a) prevent backflow of hydraulic fluid to ensure pressure stability of the hydraulic circuit and prevent interference between circuits during the operation of the first and second driving cylinders (S1) (S2).

[0043] A plurality of fluid passages are formed in the above valve body (110) to sequentially guide the flow of hydraulic fluid.

[0044] First, the inlet port (111) and the first valve groove (119) are connected by the first inlet passage (121). Accordingly, hydraulic fluid supplied from the hydraulic pump (1) to the inlet port (111) is guided to the first valve groove (119) through the first inlet passage (121).

[0045] The first valve groove (119) and the first spool bore (113) are connected by the first supply path (122). Accordingly, hydraulic fluid passing through the first valve groove (119) is supplied to the first spool bore (113) through the first supply path (122).

[0046] The first spool bore (113) and the first operating port (115) are connected by a first operating fluid path (123) as shown in FIG. 8. Accordingly, hydraulic fluid flowing into the first spool bore (113) is transferred to the first operating port (115) through the first operating fluid path (123) according to the position of the first spool (140) to operate the corresponding first driving cylinder (S1).

[0047] Additionally, the second operating port (117) and the first spool bore (113) are connected by the first return path (124). Accordingly, hydraulic fluid discharged after the operation of the driving cylinder (S1) flows in through the second operating port (117), passes through the first return path (124), and returns to the first spool bore (113).

[0048] The first spool bore (113) and the second spool bore (114) are connected by a first transmission path (125). The first transmission path (125) is a path for transmitting hydraulic fluid passing through the first spool bore (113) to the second spool bore (114), and plays an important role in forming a series hydraulic circuit that sequentially operates two first and second driving cylinders (S1) (S2).

[0049] Additionally, the first transmission path (125) is formed to be in communication with the second inflow path (127), and the second inflow path (127) is formed to be connected to one side (126) of the valve body (110) and simultaneously configured to be connected to the second valve groove (120). Accordingly, hydraulic fluid passing through the first spool bore (113) can be supplied to the second valve groove (120) through the first transmission path (125) and the second inflow path (127).

[0050] The second valve groove (120) and the second spool bore (114) are connected by a second supply path (128) as shown in 11. Thus, hydraulic fluid passing through the second valve groove (120) is supplied to the second spool bore (114) through the second supply path (128).

[0051] The second spool bore (114) and the third operating port (116) are connected by the second operating fluid path (129). Accordingly, hydraulic fluid flowing into the second spool bore (114) is supplied to the third operating port (116) via the second operating fluid path (129) according to the position of the second spool (140a), and operates the second driving cylinder (S2) connected to the third operating port (116).

[0052] Additionally, the fourth operating port (118) and the second spool bore (114) are connected by the second return path (130). Accordingly, hydraulic fluid discharged after operation of another driving cylinder (S2) flows in through the fourth operating port (118), passes through the second return path (130), and returns to the second spool bore (114).

[0053] The second spool bore (114) and the return port (112) are connected by a second transmission path (131). Accordingly, hydraulic fluid returned to the second spool bore (114) can be transmitted to the return port (112) through the second transmission path (131).

[0054] Additionally, the return port (112) and one side (126) of the valve body (110) are connected by a third return path (132). The third return path (132) functions as a path that guides hydraulic fluid discharged after operation from the sub-hydraulic operating valve (200) to be recovered into the hydraulic tank (2) through the return port (112).

[0055] Due to the Euro structure as described above, the main hydraulic operating valve (100) of the present invention can stably configure a series hydraulic circuit in which hydraulic fluid first operates the first driving cylinder (S1) and then is sequentially transmitted to the second driving cylinder (S2). Therefore, two first and second driving cylinders (S1) and (S2) can be sequentially controlled within a single valve body (110), thereby providing the effect of improving the operational stability and circuit continuity of the front loader.

[0056] Meanwhile, a junction groove (135) is formed in the valve body (110). The junction groove (135) is formed between the front end of the return port (112) and the carryover discharge passage (133) formed on the front of the valve body (110), and one side is connected to the side (126) of the valve body (110), and the other side is connected to the second spool bore (114) and the second carryover passage (134) via.

[0057] The above junction home (135) is not a simple groove structure, but functions as a connection part capable of switching between the state of independent use of the main hydraulic operating valve (100) and the state of connection with an external or sub hydraulic operating valve (200). That is, in this embodiment, when only the main hydraulic operating valve (100) is used, it is necessary to prevent unnecessary leakage of hydraulic fluid toward the junction home (135).

[0058] To this end, a carryover plug (160) is installed at the front end of the return port (112). The carryover plug (160) blocks hydraulic fluid flowing into the return port (112) from being discharged into the carryover discharge path (133) via the junction groove (135). Accordingly, when the main hydraulic operating valve (100) is used alone, hydraulic fluid is prevented from escaping through an unintended path, and a normal recovery flow through the return port (112) is maintained.

[0059] Additionally, an end cover (180) is attached to one side (126) of the valve body (110) by penetrating it with a fastening member (3). A closing plug (170) that fits into a junction groove (135) is integrally attached to the inner surface of the end cover (180). When the end cover (180) is coupled to the side (126) of the valve body (110), the closing plug (170) is inserted into the junction groove (135) to close the junction groove (135).

[0060] Due to the structure of the end cover (180) and the closing plug (170) as described above, when the main hydraulic operating valve (100) is used alone, the leakage of hydraulic fluid through the junction groove (135) is blocked, and the series hydraulic circuit inside the valve body (110) is stably maintained.

[0061] Accordingly, the present invention allows for the minimization of external piping, the reduction of the possibility of hydraulic leakage, and stable control of the flow of hydraulic fluid by integrally forming an inlet port (111), a return port (112), first and second spool bores (113) (114), first, second, third, and fourth operating ports (115) (116) (117) (118), first and second valve grooves (119) (120), and a plurality of fluid passages inside a valve body (110).

[0062] In addition, backflow of hydraulic fluid is prevented by the first check valve (150) and the second check valve (150a), and unnecessary leakage of hydraulic fluid is blocked by the carryover plug (160) and the closing plug (170), thereby improving the stability and reliability of the series hydraulic circuit that sequentially operates the two first and second drive cylinders (S1) (S2).

[0063] Below, the operation process of the main hydraulic operating valve (100) configured as above, in particular the hydraulic fluid flow of the series hydraulic circuit that sequentially operates the two first and second driving cylinders (S1) (S2), will be explained in detail.

[0064] First, hydraulic fluid flows into the valve body (110) through the inlet port (111) in accordance with the operation of the hydraulic pump (1). The hydraulic fluid flowing into the inlet port (111) is guided to the first valve groove (119) via the first inlet passage (121), and after passing through the first check valve (150) installed in the first valve groove (119), it is supplied to the first spool bore (113) through the first supply passage (122).

[0065] At this time, depending on the position of the first spool (140), hydraulic fluid is transferred to the first operating port (115) via the first operating fluid path (123), and accordingly, the first driving cylinder (S1) connected to the first operating port (115) is operated.

[0066] After the operation of the first driving cylinder (S1) is completed, the hydraulic fluid discharged flows back into the valve body (110) through the second operating port (117). Subsequently, the hydraulic fluid flowing into the second operating port (117) returns to the first spool bore (113) via the first return path (124), and then is transferred to the second spool bore (114) side through the first transmission path (125).

[0067] The hydraulic fluid passing through the first transmission path (125) passes through the second check valve (150a) installed in the second valve groove (120) and is then supplied to the second spool bore (114) through the second supply path (128).

[0068] At this time, depending on the position of the second spool (140a), hydraulic fluid is transferred to the third operating port (116) via the second operating fluid path (129), and accordingly, the second driving cylinder (S2) connected to the third operating port (116) is operated.

[0069] After the operation of the second driving cylinder (S2) is completed, the hydraulic fluid discharged flows into the valve body (110) through the fourth operating port (118). Subsequently, the hydraulic fluid flowing into the fourth operating port (118) returns to the second spool bore (114) via the second return path (130), and is then recovered into the hydraulic tank (2) through the return port (112).

[0070] By means of such a series of hydraulic fluid flows, the main hydraulic operating valve (100) of the present invention can stably implement a series hydraulic circuit that sequentially operates the first driving cylinder (S1) and the second driving cylinder (S2).

[0071] In particular, hydraulic fluid passing through the first driving cylinder (S1) via the first transmission path (125) is continuously supplied to the second driving cylinder (S2), thereby allowing hydraulic fluid transmission between multiple driving cylinders to be continuous without interruption, and thus enabling stable operation and consistent power transmission during front loader operation.

[0072] In addition, since backflow of hydraulic fluid is prevented by the first check valve (150) and the second check valve (150a), interference between circuits is minimized during the operation of each driving cylinder and pressure stability of the hydraulic circuit is improved.

[0074] Meanwhile, the present invention may further include a carryover structure that allows hydraulic fluid supplied from the hydraulic pump (1) to be continuously delivered to an external hydraulic control valve even when the first spool (140) and the second spool (140a) are in a non-operating state.

[0075] To this end, the closing plug (170) integrally formed in the end cover (180) has a discharge channel (171) formed at one end that communicates with the second carryover channel (134), and a plurality of discharge holes (172) communicating with the discharge channel (171) are formed radially through the outer surface.

[0076] The above discharge holes (172) may be formed in multiple numbers along the circumferential direction of the outer surface of the closing plug (170), and accordingly, hydraulic fluid delivered through the second carryover path (134) may flow smoothly into the discharge path (171) inside the closing plug (170) and then be discharged toward the carryover discharge path (133).

[0077] Specifically, when the first spool (140) and the second spool (140a) are in a non-operating state, the hydraulic fluid flowing into the inlet port (111) sequentially passes through the first carryover path (136), the first spool bore (113), the first transfer path (125), the second spool bore (114), and the second carryover path (134), which are formed to connect the inlet port (111) and the first spool bore (113).

[0078] Afterward, the hydraulic fluid passing through the second carryover path (134) passes through the discharge path (171) and discharge hole (172) of the closing plug (170) and is supplied to the external hydraulic control valve through the carryover discharge path (133).

[0079] Accordingly, the present invention provides the effect of ensuring the continuity of hydraulic supply to an external working device or additional hydraulic device, so that even when the spools of the main hydraulic operating valve (100) are in a non-operating state, the flow of hydraulic fluid is not blocked and can continue to be transmitted to an external hydraulic control valve.

[0080] In addition, by forming a discharge passage (171) and a radial discharge hole (172) in the closing plug (170), a carryover passage can be formed without separate complex external piping, thereby simplifying the valve structure while improving the hydraulic fluid supply efficiency and system scalability.

[0082] Next, the present invention may include a circuit switching structure that allows a sub hydraulic operating valve (200) to be selectively coupled to a main hydraulic operating valve (100) to form a parallel hydraulic circuit.

[0083] To this end, a junction groove (135) is formed on one side (126) of the valve body (110), and a circuit switching junction (300) can be inserted into the junction groove (135).

[0084] Specifically, after separating the end cover (180) from the valve body (110), a circuit switching junction (300) is inserted in the forward direction into the junction groove (135), and the installation position of the first plug (400) is changed, so that a sub hydraulic operating valve (200) can be assembled on the side of the valve body (110).

[0085] As shown in FIGS. 17 and 18, the above circuit switching junction (300) has a hydraulic fluid discharge path (301) formed in a recess in the center of the outer surface, a discharge path (302) that penetrates both sides in the center, an inflow path (303) formed in a recess on the outer surface that contacts one end, and a plurality of inflow holes (304) communicating with the discharge path (302) are formed radially in the inflow path (303). In particular, an O-ring (306) is fitted into the ring groove (305) formed on both outer surfaces of the hydraulic fluid discharge path (301) to seal the gap with the inner surface of the junction groove (135), thereby preventing leakage of hydraulic fluid, allowing the hydraulic fluid to flow stably along the set path, minimizing pressure loss between circuits, and providing the effect of improving the operational reliability of the hydraulic system.

[0086] At this time, the circuit switching junction (300) is inserted in a forward direction such that the inflow path (303) faces the side (126) of the valve body (110), and is configured so that the hydraulic fluid flow path is established by coupling with the first plug (400).

[0087] Additionally, the first plug (400) penetrates the upper surface of the valve body (110) and is connected to the second inlet passage (127), and is also screw-coupled to the lower part of the third transmission passage (137) connected to the second transmission passage (131) adjacent to the junction groove (135). Accordingly, the hydraulic fluid passing through the second inlet passage (127) is blocked from flowing into the circuit switching junction (300), and the flow of hydraulic fluid is selectively controlled.

[0088] In addition, a plug bolt (137a) is screw-coupled to the upper part of the third transmission channel (137) to prevent hydraulic leakage from the upper part of the third transmission channel (137) and at the same time ensure the stability of the hydraulic flow.

[0089] With this configuration, hydraulic fluid flowing inside the main hydraulic operating valve (100) is continuously transmitted along the first transmission path (125) and the second transmission path (131), and the series hydraulic circuit of the main hydraulic operating valve (100) is stably maintained by blocking the inflow of hydraulic fluid to the sub hydraulic operating valve (200) side by the combination of the first plug (400) and the circuit switching junction (300).

[0090] Accordingly, the sub hydraulic operating valve (200) forms a parallel hydraulic circuit connected in parallel with the main hydraulic operating valve (100), and can independently drive a separate third driving cylinder (S3).

[0091] Therefore, since the present invention can simply implement a parallel hydraulic circuit by changing only the insertion direction of the circuit switching junction (300) and the installation position of the first plug (400), multiple work members can be controlled simultaneously or independently, and work efficiency and operational convenience can be improved.

[0093] In the following, when the circuit switching junction (300) is inserted in the forward direction as described above and the installation position of the first plug (400) is changed, a parallel hydraulic circuit is formed in which the main hydraulic operating valve (100) and the sub hydraulic operating valve (200) are connected in parallel, and the hydraulic fluid flow at this time is described.

[0094] First, hydraulic fluid flowing into the inlet port (111) according to the operation of the hydraulic pump (1) passes through the first inlet path (121), passes through the first check valve (150), then sequentially passes through the first supply path (122), the first spool bore (113), and the first operating path (123), and is supplied to the first driving cylinder (S1) through the first operating port (115).

[0095] The hydraulic fluid discharged after the operation of the first driving cylinder (S1) flows into the second operating port (117) and is transmitted through the first return path (124) and the first spool bore (113) via the first transmission path (125).

[0096] The hydraulic fluid passing through the first transmission path (125) passes through the second check valve (150a), and a portion of the branched hydraulic fluid passes through the second inlet path (127) to be supplied to the sub hydraulic operating valve (200), while the remaining hydraulic fluid continues to be transmitted along the series hydraulic circuit of the main hydraulic operating valve (100) through the second supply path (128) and the second spool bore (114).

[0097] The hydraulic fluid supplied to the sub hydraulic operating valve (200) passes through the third check valve (201) and then through the third spool bore (202) to be supplied to the third driving cylinder (S3). After the operation of the third driving cylinder (S3), the hydraulic fluid discharged passes through the third spool bore (202) and then flows into the return port (112) through the third return path (132) of the main hydraulic operating valve (100) and is recovered into the hydraulic tank (2).

[0098] Meanwhile, the remaining hydraulic fluid passing through the first transmission path (125) passes through the second check valve (150a) and then sequentially passes through the second supply path (128), the second spool bore (114), and the second operating path (129) to be supplied to the second driving cylinder (S2) through the third operating port (116).

[0099] After the operation of the second drive cylinder (S2), the hydraulic fluid discharged flows into the fourth operating port (118), passes through the second return path (130) and the second spool bore (114) to flow into the return port (112), and is then recovered into the hydraulic tank (2).

[0100] Due to such hydraulic fluid flow, in the present invention, the main hydraulic operating valve (100) can maintain a series hydraulic circuit that sequentially operates the first and second driving cylinders (S1) and (S2), while simultaneously forming a parallel hydraulic circuit that independently operates the third driving cylinder (S3) in the sub hydraulic operating valve (200) using hydraulic fluid branched from the first transmission path (125).

[0101] Therefore, since the present invention can simultaneously implement a series hydraulic circuit and a parallel hydraulic circuit in a single main hydraulic operating valve (100) structure, it can control multiple working members independently and efficiently and provide a hydraulic control system capable of responding to various working environments.

[0103] Furthermore, the present invention may further include a circuit switching structure for connecting a sub hydraulic operating valve (200) to a main hydraulic operating valve (100) in a continuous series hydraulic circuit, and the configuration and operation thereof will be described.

[0104] To this end, after separating the end cover (180), the circuit switching junction (300) is inserted in the reverse direction into the junction groove (135), and the installation position of the first plug (400) is changed, and the second plug (500) is additionally installed.

[0105] At this time, the circuit switching junction (300) is inserted in the reverse direction into the junction groove (135) such that the inflow path (303) faces the second carryover path (134) side, as shown in FIG. 19.

[0106] Additionally, the first plug (400) is screw-coupled to the second inlet passage (127) located between the second valve groove (120) and the third transmission passage (137), and the third transmission passage (137) is formed to penetrate the upper surface of the valve body (110) to be connected to the second inlet passage (127) and also to be connected to the second transmission passage (131) adjacent to the junction groove (135).

[0107] Accordingly, the hydraulic fluid passing through the first transmission path (125) is blocked from flowing into the sub-hydraulic operating valve (200) through the second inflow path (127), and the entire amount of hydraulic fluid passes through the second check valve (150a) and proceeds to the internal path of the main hydraulic operating valve (100).

[0108] In addition, the second plug (500) is installed on the rear return port (112) side of the carryover plug (160) to prevent hydraulic fluid passing through the second transmission path (131) from being recovered early into the hydraulic tank (2) through the return port (112), and to force the path so that the hydraulic fluid is continuously transmitted to the sub hydraulic operating valve (200) through the junction groove (135) and the circuit switching junction (300).

[0109] With this configuration, the main hydraulic operating valve (100) and the sub hydraulic operating valve (200) are converted into a continuous series hydraulic circuit rather than a simple parallel connection.

[0110] Below, the hydraulic fluid flow in the state configured as described above will be explained.

[0111] First, hydraulic fluid flowing into the inlet port (111) according to the operation of the hydraulic pump (1) passes sequentially through the first inlet path (121), the first check valve (150), the first supply path (122), the first spool bore (113), and the first operating path (123), and is supplied to the first driving cylinder (S1) through the first operating port (115).

[0112] The hydraulic fluid discharged after the operation of the first driving cylinder (S1) flows in through the second operating port (117), passes through the first return path (124), the first spool bore (113), and the first transmission path (125), then passes through the second check valve (150a) and is delivered to the second supply path (128) and the second spool bore (114).

[0113] At this time, since the branching inflow through the second inflow path (127) is blocked by the first plug (400), the hydraulic fluid is not branched to the sub hydraulic operating valve (200) and is continuously delivered along the series path of the main hydraulic operating valve (100).

[0114] The above hydraulic fluid operates the second driving cylinder (S2) through the third operating port (116) via the second spool bore (114) and the second operating fluid path (129), and is then discharged through the fourth operating port (118) and delivered to the second transmission fluid path (131) via the second return fluid path (130) and the second spool bore (114).

[0115] Afterwards, the hydraulic fluid passing through the second transmission path (131) flows into the junction groove (135) while the outflow to the return port (112) is blocked by the second plug (500) as shown in FIG. 24, and is supplied to the sub hydraulic operating valve (200) by sequentially passing through the inflow path (303), a plurality of inflow holes (304), and the discharge path (302) of the circuit switching junction (300).

[0116] The hydraulic fluid flowing into the sub hydraulic operating valve (200) passes through the third check valve (201) and then through the third spool bore (202) to operate the third driving cylinder (S3), and the hydraulic fluid discharged after the operation of the third driving cylinder (S3) flows back into the return port (112) through the third return path (132) of the main hydraulic operating valve (100) and is recovered into the hydraulic tank (2).

[0117] By means of such hydraulic fluid flow, the present invention can form a continuous series hydraulic circuit in which hydraulic fluid is sequentially delivered from the main hydraulic operating valve (100) to the sub hydraulic operating valve (200), and can implement an expandable hydraulic system that operates a plurality of driving cylinders in stages.

[0118] Accordingly, the present invention provides the advantage of being able to flexibly respond to various working environments, as it allows for selective switching between a parallel hydraulic circuit and a series hydraulic circuit through simple operations such as changing the insertion direction of the circuit switching junction (300), the installation position of the first plug (400), and the installation of the second plug (500), as well as expanding by continuously connecting a plurality of hydraulic operating valves.

[0119] Meanwhile, the present invention may further include a carryover hydraulic flow that allows hydraulic fluid to be continuously supplied to an external hydraulic control valve even when the first spool (140), the second spool (140a), and the third spool (210) are all in a non-operational state, and this will be explained.

[0120] In the above non-operational state, hydraulic fluid flowing from the hydraulic pump (1) into the inlet port (111) flows into the first spool bore (113) along the first carryover path (136), and then is transferred to the second carryover path (134) via the first transfer path (125).

[0121] Subsequently, the hydraulic fluid passing through the second carryover path (134) passes through the discharge path (302) of the circuit switching junction (300) and flows into the third spool bore (202) of the sub hydraulic operating valve (200). At this time, since the third spool (210) of the sub hydraulic operating valve (200) is also in a non-operating state, the hydraulic fluid simply passes through the inside of the sub hydraulic operating valve (200).

[0122] Then, the hydraulic fluid passing through the sub hydraulic operating valve (200) passes through the third carryover passage (138) formed to connect the upper part of the junction groove (135) of the main hydraulic operating valve (100) and the side (126) of the valve body (110), and then passes through the hydraulic fluid discharge passage (301) formed on the outer surface of the circuit switching junction (300) to the carryover discharge passage (133), and finally, the hydraulic fluid is supplied to the external hydraulic control valve through the carryover discharge passage (133).

[0123] Due to this hydraulic fluid flow, the present invention ensures that the flow of hydraulic fluid is not interrupted even when the spools of the main hydraulic operating valve (100) and the sub hydraulic operating valve (200) are not operating, and allows the fluid to be continuously transmitted from the main hydraulic operating valve (100) through the sub hydraulic operating valve (200) and then back through the main hydraulic operating valve (100) to the external hydraulic control valve.

[0124] Accordingly, the present invention provides the effect of enabling the stable maintenance of the supply of hydraulic fluid even in a system in which a plurality of hydraulic operating valves are connected in series or parallel, and enabling the continuous operation of additional hydraulic devices. Explanation of the symbols

[0125] S1: First driving cylinder S2: Second driving cylinder S3: 3rd driving cylinder 1: Hydraulic pump 2: Hydraulic tank 100: Main hydraulic control valve 110: Valve body 111: Inlet port 112: Return port 113: First spool bore 114: Second spool bore 115: First operating port 116: 3rd operating port 117: 2nd operating port 118: 4th operating port 119: 1st valve groove 120: Second valve groove 121: First inlet passage 122: First supply path 123: First operating path 124: 1st return Euro 125: 1st transfer Euro 126: Side 127: Second inflow channel 128: Second supply path 129: Second operating path 130: 2nd return Euro 131: 2nd transfer Euro 132: 3rd return euro 133: Carryover discharge euro 134: Euro for 2nd carryover 135: Junction Home 136: 1st carryover Euro 137: 3rd transfer Euro 138: Euro for 3rd carryover 140: 1st spool 140a: 2nd spool 150: 1st check valve 150a: Second check valve 160: Carryover plug 170: Close plug 171, 302: Discharge path 172: Discharge port 180: End cover 200: Sub-hydraulic operating valve 201: Third check valve 202: 3rd Spool Bore 210: 3rd Spool 300: Circuit switching junction 301: Hydraulic fluid discharge path 303: Inflow channel 304: Inflow hole 400: 1st plug 500: 2nd plug S1: First driving cylinder S2: Second driving cylinder S3: Third driving cylinder

Claims

Claim 1 A main hydraulic operating valve (100); wherein the main hydraulic operating valve (100) comprises, for forming a series hydraulic circuit to sequentially operate two first and second driving cylinders (S1) and (S2), an inlet port (111) and a return port (112) formed respectively on both sides of the lower rear of the valve body (110), a first spool bore (113) and a second spool bore (114) formed penetrating the front and rear of the valve body (110) between the inlet port (111) and the return port (112), a first operating port (115) and a third operating port (116) formed respectively on the rear of the valve body (110) above the first spool bore (113) and the second spool bore (114), and a valve body (110) formed respectively on the rear of the valve body (110) above the inlet port (111) and the return port (112). A second operating port (117) and a fourth operating port (118), a first valve groove (119) and a second valve groove (120) formed respectively on the upper surface of the upper valve body (110) of the first spool bore (113) and the second spool bore (114), a first inflow path (121) formed to connect the inflow port (111) and the first valve groove (119), a first supply path (122) formed to connect the first valve groove (119) and the first spool bore (113), a first operating path (123) formed to connect the first spool bore (113) and the first operating port (115), a first return path (124) formed to connect the second operating port (117) and the first spool bore (113), and the first spool bore (113) and A first transmission path (125) formed to connect the second spool bore (114), a second inflow path (127) formed to connect the first transmission path (125) and one side (126) of the valve body (110) and also connected to the second valve groove (120), a second supply path (128) formed to connect the second valve groove (120) and the second spool bore (114), and a second operating path (129) formed to connect the second spool bore (114) and the third operating port (116).A second return path (130) formed to connect the fourth operating port (118) and the second spool bore (114), a second transmission path (131) formed to connect the second spool bore (114) and the return port (112), and a third return path (132) formed to connect the return port (112) and one side (126) of the valve body (110). The above-mentioned return port (112) is formed between the front end of the return port (112) and the front end of the valve body (110) and the carryover discharge passage (133), and is configured to include a junction groove (135) which has one side connected to the side (126) of the valve body (110) and the other side connected via the second spool bore (114) and the second carryover passage (134); a first spool (140) and a second spool (140a) that are respectively movably installed in the first spool bore (113) and the second spool bore (114) to operate the corresponding first and second driving cylinders (S1) and (S2); a first check valve (150) and a second check valve (150a) that are respectively installed in the first valve groove (119) and the second valve groove (120) to prevent backflow of hydraulic fluid; and installed at the front end of the return port (112). The device comprises a carryover plug (160) that blocks hydraulic fluid flowing into the return port (112) from being discharged through the junction groove (135) to the carryover discharge path (133); and an end cover (180) that is attached to one side (126) of the valve body (110) and has a closing plug (170) integrally attached to its inner surface that fits into the junction groove (135); hydraulic fluid flowing into the inlet port (111) according to the operation of the hydraulic pump (1) flows into the inlet port (111), and the hydraulic fluid flowing into the inlet port (111) flows through the first inlet path (121), passes through the first check valve (150), then sequentially passes through the first supply path (122), the first spool bore (113), and the first operating path (123), and is supplied to the first driving cylinder (S1) through the first operating port (115).The hydraulic fluid discharged after the operation of the first driving cylinder (S1) flows into the second operating port (117); the hydraulic fluid flowing into the second operating port (117) passes through the first return path (124), the first spool bore (113), and the first transmission path (125), passes through the second check valve (150a), then sequentially passes through the second supply path (128), the second spool bore (114), and the second operating path (129), and is supplied to the second driving cylinder (S2) through the third operating port (116); the hydraulic fluid discharged after the operation of the second driving cylinder (S2) flows into the fourth operating port (118); the hydraulic fluid flowing into the fourth operating port (118) passes sequentially through the second return path (130) and the second spool bore (114) to the return port (112). Hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor, characterized by being returned to a hydraulic tank (2) after being introduced. Claim 2 delete Claim 3 A main hydraulic operating valve (100); wherein the main hydraulic operating valve (100) comprises, for forming a series hydraulic circuit to sequentially operate two first and second driving cylinders (S1) and (S2), an inlet port (111) and a return port (112) formed respectively on both sides of the lower rear of the valve body (110), a first spool bore (113) and a second spool bore (114) formed penetrating the front and rear of the valve body (110) between the inlet port (111) and the return port (112), a first operating port (115) and a third operating port (116) formed respectively on the rear of the valve body (110) above the first spool bore (113) and the second spool bore (114), and a valve body (110) formed respectively on the rear of the valve body (110) above the inlet port (111) and the return port (112). A second operating port (117) and a fourth operating port (118), a first valve groove (119) and a second valve groove (120) formed respectively on the upper surface of the upper valve body (110) of the first spool bore (113) and the second spool bore (114), a first inflow path (121) formed to connect the inflow port (111) and the first valve groove (119), a first supply path (122) formed to connect the first valve groove (119) and the first spool bore (113), a first operating path (123) formed to connect the first spool bore (113) and the first operating port (115), a first return path (124) formed to connect the second operating port (117) and the first spool bore (113), and the first spool bore (113) and A first transmission path (125) formed to connect the second spool bore (114), a second inflow path (127) formed to connect the first transmission path (125) and one side (126) of the valve body (110) and also connected to the second valve groove (120), a second supply path (128) formed to connect the second valve groove (120) and the second spool bore (114), and a second operating path (129) formed to connect the second spool bore (114) and the third operating port (116).A second return path (130) formed to connect the fourth operating port (118) and the second spool bore (114), a second transmission path (131) formed to connect the second spool bore (114) and the return port (112), and a third return path (132) formed to connect the return port (112) and one side (126) of the valve body (110). The above-mentioned return port (112) is formed between the front end of the return port (112) and the front end of the valve body (110) and the carryover discharge passage (133), and is configured to include a junction groove (135) which has one side connected to the side (126) of the valve body (110) and the other side connected via the second spool bore (114) and the second carryover passage (134); a first spool (140) and a second spool (140a) that are respectively movably installed in the first spool bore (113) and the second spool bore (114) to operate the corresponding first and second driving cylinders (S1) and (S2); a first check valve (150) and a second check valve (150a) that are respectively installed in the first valve groove (119) and the second valve groove (120) to prevent backflow of hydraulic fluid; and installed at the front end of the return port (112). The system comprises a carryover plug (160) that blocks hydraulic fluid flowing into the return port (112) from being discharged into the carryover discharge path (133) via the junction groove (135); and an end cover (180) that is attached to one side (126) of the valve body (110) and has a closing plug (170) integrally attached to its inner surface that fits into the junction groove (135); wherein the closing plug (170) has a discharge path (171) formed at one end that communicates with the second carryover path (134), and a plurality of discharge holes (172) communicating with the discharge path (171) are formed radially through the outer surface; and when the first spool (140) and the second spool (140a) are in a non-operating state, the hydraulic fluid flowing into the inlet port (111) is discharged into the first carryover path (136), the first Spool bore (113), first transmission channel (125), second spool bore (114),A hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor, characterized by sequentially passing through the second carryover path (134), passing through the discharge path (171) and discharge hole (172), and then being supplied to an external hydraulic control valve through the carryover discharge path (133). Claim 4 A main hydraulic operating valve (100); wherein the main hydraulic operating valve (100) comprises, for forming a series hydraulic circuit to sequentially operate two first and second driving cylinders (S1) and (S2), an inlet port (111) and a return port (112) formed respectively on both sides of the lower rear of the valve body (110), a first spool bore (113) and a second spool bore (114) formed penetrating the front and rear of the valve body (110) between the inlet port (111) and the return port (112), a first operating port (115) and a third operating port (116) formed respectively on the rear of the valve body (110) above the first spool bore (113) and the second spool bore (114), and a valve body (110) formed respectively on the rear of the valve body (110) above the inlet port (111) and the return port (112). A second operating port (117) and a fourth operating port (118), a first valve groove (119) and a second valve groove (120) formed respectively on the upper surface of the upper valve body (110) of the first spool bore (113) and the second spool bore (114), a first inflow path (121) formed to connect the inflow port (111) and the first valve groove (119), a first supply path (122) formed to connect the first valve groove (119) and the first spool bore (113), a first operating path (123) formed to connect the first spool bore (113) and the first operating port (115), a first return path (124) formed to connect the second operating port (117) and the first spool bore (113), and the first spool bore (113) and A first transmission path (125) formed to connect the second spool bore (114), a second inflow path (127) formed to connect the first transmission path (125) and one side (126) of the valve body (110) and also connected to the second valve groove (120), a second supply path (128) formed to connect the second valve groove (120) and the second spool bore (114), and a second operating path (129) formed to connect the second spool bore (114) and the third operating port (116).A second return path (130) formed to connect the fourth operating port (118) and the second spool bore (114), a second transmission path (131) formed to connect the second spool bore (114) and the return port (112), and a third return path (132) formed to connect the return port (112) and one side (126) of the valve body (110). The above-mentioned return port (112) is formed between the front end of the return port (112) and the front end of the valve body (110) and the carryover discharge passage (133), and is configured to include a junction groove (135) which has one side connected to the side (126) of the valve body (110) and the other side connected via the second spool bore (114) and the second carryover passage (134); a first spool (140) and a second spool (140a) that are respectively movably installed in the first spool bore (113) and the second spool bore (114) to operate the corresponding first and second driving cylinders (S1) and (S2); a first check valve (150) and a second check valve (150a) that are respectively installed in the first valve groove (119) and the second valve groove (120) to prevent backflow of hydraulic fluid; and installed at the front end of the return port (112). A carryover plug (160) that blocks hydraulic fluid flowing into the return port (112) from being discharged through the junction groove (135) to the carryover discharge path (133); and an end cover (180) that is attached to one side (126) of the valve body (110) and has a closing plug (170) integrally attached to its inner surface that fits into the junction groove (135); and after separating the end cover (180), a circuit switching junction (300) is inserted in the forward direction into the junction groove (135), and by changing the installation position of the first plug (400), the sub hydraulic operating valve (200) assembled on the side of the main hydraulic operating valve (100) is switched to a parallel hydraulic circuit; and the circuit switching junction (300) has a hydraulic fluid discharge path (301) formed in a recess in the center of its outer surface, and a passage penetrating both sides in the center A discharge channel (302) is formed,A plurality of inlet holes (304) communicating with the discharge passage (302) are radially formed in an inlet passage (303) formed in a recess on the outer surface contacting one end, and the inlet passage (303) is inserted in the forward direction into the junction groove (135) so as to be located on one side (126) of the valve body (110); the first plug (400) penetrates the upper surface of the valve body (110) and is connected to the second inlet passage (127), and is also screw-coupled to the lower part of the third transmission passage (137) connected to the second transmission passage (131) adjacent to the junction groove (135), thereby preventing hydraulic fluid passing through the second inlet passage (127) from flowing into the circuit switching junction (300), and a plug bolt (137a) is screw-coupled to the upper part of the third transmission passage (137), characterized by having a multi-circuit front for an agricultural tractor. Hydraulic operating valve for loaders. Claim 5 In claim 4, hydraulic fluid resulting from the operation of the hydraulic pump (1) flows into the inlet port (111), and the hydraulic fluid flowing into the inlet port (111) passes through the first inlet passage (121), passes through the first check valve (150), then sequentially passes through the first supply passage (122), the first spool bore (113), and the first operating passage (123), and is supplied to the first driving cylinder (S1) through the first operating port (115); and the hydraulic fluid discharged after the operation of the first driving cylinder (S1) flows into the second operating port (117); and the hydraulic fluid flowing into the second operating port (117) passes through the first return passage (124), the first spool bore (113), and the first transmission passage (125), passes through the second check valve (150a), then passes through the second supply passage (128), and the second Hydraulic fluid is supplied to the second driving cylinder (S2) through the third operating port (116) by sequentially passing through the spool bore (114) and the second operating fluid path (129); hydraulic fluid discharged after operation of the second driving cylinder (S2) flows into the fourth operating port (118); hydraulic fluid flowing into the fourth operating port (118) flows into the return port (112) by sequentially passing through the second return fluid path (130) and the second spool bore (114) and is recovered into the hydraulic tank (2); hydraulic fluid passing through the first transmission fluid path (125) passes through the second check valve (150a), and a portion of the branched hydraulic fluid passes through the second inflow fluid path (127) and is supplied to the sub hydraulic operating valve (200); hydraulic fluid flowing into the sub hydraulic operating valve (200) passes through the third check valve (201). After passing through, it is supplied to the third driving cylinder (S3) via the third spool bore (202), and the hydraulic fluid discharged after the operation of the third driving cylinder (S3) flows into the return port (112) through the third return path (132) of the main hydraulic operating valve (100) via the third spool bore (202) and is recovered into the hydraulic tank (2);A hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor, characterized in that the main hydraulic operating valve (100) is configured to form a series hydraulic circuit and the sub hydraulic operating valve (200) is configured to form a parallel hydraulic circuit.; Claim 6 A main hydraulic operating valve (100); wherein the main hydraulic operating valve (100) comprises, for forming a series hydraulic circuit to sequentially operate two first and second driving cylinders (S1) and (S2), an inlet port (111) and a return port (112) formed respectively on both sides of the lower rear of the valve body (110), a first spool bore (113) and a second spool bore (114) formed penetrating the front and rear of the valve body (110) between the inlet port (111) and the return port (112), a first operating port (115) and a third operating port (116) formed respectively on the rear of the valve body (110) above the first spool bore (113) and the second spool bore (114), and a valve body (110) formed respectively on the rear of the valve body (110) above the inlet port (111) and the return port (112). A second operating port (117) and a fourth operating port (118), a first valve groove (119) and a second valve groove (120) formed respectively on the upper surface of the upper valve body (110) of the first spool bore (113) and the second spool bore (114), a first inflow path (121) formed to connect the inflow port (111) and the first valve groove (119), a first supply path (122) formed to connect the first valve groove (119) and the first spool bore (113), a first operating path (123) formed to connect the first spool bore (113) and the first operating port (115), a first return path (124) formed to connect the second operating port (117) and the first spool bore (113), and the first spool bore (113) and A first transmission path (125) formed to connect the second spool bore (114), a second inflow path (127) formed to connect the first transmission path (125) and one side (126) of the valve body (110) and also connected to the second valve groove (120), a second supply path (128) formed to connect the second valve groove (120) and the second spool bore (114), and a second operating path (129) formed to connect the second spool bore (114) and the third operating port (116).A second return path (130) formed to connect the fourth operating port (118) and the second spool bore (114), a second transmission path (131) formed to connect the second spool bore (114) and the return port (112), and a third return path (132) formed to connect the return port (112) and one side (126) of the valve body (110). The above-mentioned return port (112) is formed between the front end of the return port (112) and the front end of the valve body (110) and the carryover discharge passage (133), and is configured to include a junction groove (135) which has one side connected to the side (126) of the valve body (110) and the other side connected via the second spool bore (114) and the second carryover passage (134); a first spool (140) and a second spool (140a) that are respectively movably installed in the first spool bore (113) and the second spool bore (114) to operate the corresponding first and second driving cylinders (S1) and (S2); a first check valve (150) and a second check valve (150a) that are respectively installed in the first valve groove (119) and the second valve groove (120) to prevent backflow of hydraulic fluid; and installed at the front end of the return port (112). A carryover plug (160) that blocks hydraulic fluid flowing into the return port (112) from being discharged through the junction groove (135) to the carryover discharge path (133); and an end cover (180) that is attached to one side (126) of the valve body (110) and has a closing plug (170) integrally attached to its inner surface that fits into the junction groove (135); and after separating the end cover (180), a circuit switching junction (300) is inserted in the reverse direction into the junction groove (135), and the installation position of the first plug (400) is changed, and the second plug (500) is installed so that the sub hydraulic operating valve (200) assembled on the side of the main hydraulic operating valve (100) is switched to a series hydraulic circuit; and the circuit switching junction (300) has a hydraulic fluid discharge path (301) formed in the center of its outer surface, and A discharge channel (302) is formed in the center that penetrates both sides, andIn the inlet passage (303) formed by a recess on the outer surface contacting one end, a plurality of inlet holes (304) communicating with the discharge passage (302) are formed radially, and the inlet passage (303) is inserted in the reverse direction into the junction groove (135) so as to be positioned toward the second carryover passage (134); the first plug (400) penetrates the upper surface of the valve body (110) and is connected to the second inlet passage (127), and is also screw-coupled to the second inlet passage (127) located between the second valve groove (120) and the third transmission passage (137) connected to the second transmission passage (131) adjacent to the junction groove (135), so that the entire amount of hydraulic fluid passing through the first transmission passage (125) passes through the second check valve (150a) and is prevented from flowing into the sub hydraulic operating valve (200); and the second A hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor, characterized in that the plug (500) is installed at the rear return port (112) of the carryover plug (160) to prevent hydraulic fluid passing through the second transmission path (127) from being recovered into the hydraulic tank (2) through the return port (112). Claim 7 In claim 6, hydraulic fluid resulting from the operation of the hydraulic pump (1) flows into the inlet port (111), and the hydraulic fluid flowing into the inlet port (111) passes through the first inlet path (121), passes through the first check valve (150), then sequentially passes through the first supply path (122), the first spool bore (113), and the first operating path (123), and is supplied to the first driving cylinder (S1) through the first operating port (115); and the hydraulic fluid discharged after the operation of the first driving cylinder (S1) flows into the second operating port (117); and the hydraulic fluid flowing into the second operating port (117) passes through the first return path (124), the first spool bore (113), and the first transmission path (125), passes through the second check valve (150a), then passes through the second supply path (128), and the second Hydraulic fluid is supplied to the second driving cylinder (S2) through the third operating port (116) by sequentially passing through the spool bore (114) and the second operating fluid path (129), and hydraulic fluid discharged after operation of the second driving cylinder (S2) flows into the fourth operating port (118); hydraulic fluid flowing into the fourth operating port (118) flows into the junction groove (135) by sequentially passing through the second return fluid path (130), the second spool bore (114), and the second transmission fluid path (131), and then flows into the sub hydraulic operating valve (200) by passing through the inflow fluid path (303), a plurality of inflow holes (304), and the discharge fluid path (302) of the circuit switching junction (300), and hydraulic fluid flowing into the sub hydraulic operating valve (200) passes through the third check valve (201) and then the third Hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor, characterized in that the hydraulic fluid is supplied to a third driving cylinder (S3) via a spool bore (202), and the hydraulic fluid discharged after operation of the third driving cylinder (S3) flows into the return port (112) via the third return passage (132) of the main hydraulic operating valve (100) via the third spool bore (202) and is recovered into the hydraulic tank (2); and the main hydraulic operating valve (100) and the sub hydraulic operating valve (200) are configured to form a continuous series hydraulic circuit. Claim 8 In claim 4 or 6, when the first spool (140), second spool (140a) and third spool (210) are in a non-operating state, the hydraulic fluid flowing into the inlet port (111) sequentially passes through the first carryover path (136), the first spool bore (113), the first transmission path (125), and the second carryover path (134), passes through the discharge path (302) of the circuit switching junction (300), passes through the third spool bore (202) of the sub hydraulic operating valve (200), and then sequentially passes through the third carryover path (138) formed to connect the upper part of the junction groove (135) of the main hydraulic operating valve (100) and the side (126) of the valve body (110), and the hydraulic fluid discharge path (301) formed in the circuit switching junction (300). Hydraulic operating valve for a front loader having a multi-circuit for an agricultural tractor, characterized by being supplied to an external hydraulic control valve via a carryover discharge path (133).

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