Hydraulic circuit, loader, and working machine

Abstract

A hydraulic circuit includes a locking cylinder to elongate and contract to switch between a fixed state in which a bucket is fixed to a front loader and a released state in which fixing of the bucket to the front loader is canceled, a first locking oil passage through which the hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the fixed state, a second locking oil passage through which the hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the released state, and a connecting oil passage that connects the first locking oil passage and the second locking oil passage, and includes a throttle portion to adjust a flow rate of the hydraulic oil flowing between the first locking oil passage and the second locking oil passage.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to Japanese Patent Application No. 2025-054725 filed on Mar. 28, 2025. The entire contents of this application are hereby incorporated herein by reference.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present disclosure relates to hydraulic circuits, loaders, and working machines.2. Description of the Related Art

[0003] Conventionally, a technique for working machines each including a loader to which an attachment can be detachably attached is known. As the loader, there is one to which an attachment can be detachably attached, with a cylinder being elongated and contracted by hydraulic pressure. For example, JP 2024-126696 A discloses such a configuration.

[0004] JP 2024-126696 A discloses a working vehicle that includes a working device (a loader) having a bucket as an attachment. In the working vehicle, the bucket is attached to the working device through a quick hitch provided at the tip end of an arm of the working device. The quick hitch includes a quick cylinder that elongates and contracts by hydraulic pressure of hydraulic oil. In the working vehicle, the quick cylinder is elongated to lock the quick hitch with respect to the bucket, and the quick cylinder is contracted to release the lock of the quick hitch with respect to the bucket.

[0005] Here, with the quick hitch disclosed in JP 2024-126696 A, there is a possibility that the quick cylinder will contract in a case where the hydraulic oil leaks from a valve. In this case, there is a possibility that the lock of the quick hitch will be unintentionally released, and the bucket will be detached from the quick hitch.SUMMARY OF THE INVENTION

[0006] Example embodiments of the present disclosure provide hydraulic circuits, loaders, and working machines each capable of preventing unintended detachment of an attachment.

[0007] A hydraulic circuit according to an example embodiment of the present disclosure includes a locking cylinder to elongate and contract to switch between a fixed state in which an attachment is fixed to a loader and a released state in which fixing of the attachment to the loader is canceled, a first locking oil passage through which hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the fixed state, a second locking oil passage through which the hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the released state, and a connecting oil passage that connects the first locking oil passage and the second locking oil passage, and includes a throttle portion to adjust a flow rate of the hydraulic oil flowing between the first locking oil passage and the second locking oil passage.

[0008] According to an example embodiment of the present disclosure, unintended detachment of the attachment is prevented.

[0009] A hydraulic circuit according to an example embodiment of the present disclosure further includes a shut-off valve to restrict flowing of the hydraulic oil in the first locking oil passage, and the connecting oil passage is connected to the side of the feed source of the hydraulic oil with respect to the shut-off valve in the first locking oil passage.

[0010] According to an example embodiment of the present disclosure, unintended elongation of the locking cylinder is prevented.

[0011] A hydraulic circuit according to an example embodiment of the present disclosure further includes a switching valve to switch between a state in which the hydraulic oil from the feed source is fed to the side of the locking cylinder, and a state in which the hydraulic oil is fed to the side of another cylinder different from the locking cylinder, and another oil passage through which the hydraulic oil to be fed from the switching valve to the another cylinder flows. In the hydraulic circuit, the first locking oil passage, the second locking oil passage, and the another oil passage are each connected to the switching valve.

[0012] According to an example embodiment of the present disclosure, it is possible to prevent unintended contraction of the locking cylinder due to the hydraulic oil leaking from another oil passage through the switching valve.

[0013] A loader according to an example embodiment of the present disclosure includes the hydraulic circuit according to an example embodiment of the present disclosure.

[0014] According to an example embodiment of the present disclosure, unintended detachment of the attachment is prevented.

[0015] A working machine according to an example embodiment of the present disclosure includes a loader according to an example embodiment of the present disclosure.

[0016] According to example embodiments of the present disclosure, unintended detachment of the attachment is prevented.

[0017] The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a side view showing the overall configuration of a tractor according to an example embodiment of the present disclosure.

[0019] FIG. 2A is a plan view schematically illustrating an attachment mounting mechanism and a bucket in a released state, and FIG. 2B is a plan view schematically illustrating the attachment mounting mechanism and the bucket in a fixed state.

[0020] FIG. 3 is an explanatory diagram illustrating a hydraulic circuit in a state where attachment cylinders are operable.

[0021] FIG. 4 is an explanatory diagram illustrating the hydraulic circuit in a state where a locking cylinder is operable.

[0022] FIG. 5A is an explanatory diagram illustrating the flow of hydraulic oil in a case where the locking cylinder is elongated, and FIG. 5B is an explanatory diagram illustrating the flow of hydraulic oil in a case where the locking cylinder is made to contract.

[0023] FIG. 6 is an explanatory diagram illustrating an example of a conventional hydraulic circuit.

[0024] FIG. 7A is an explanatory diagram illustrating a state in which the attachment cylinders are operable, and the hydraulic pressure on the rod side is higher than the hydraulic pressure on the bottom side of the locking cylinder, and FIG. 7B is an explanatory diagram illustrating a state in which the attachment cylinders are operable, and the hydraulic pressure on the bottom side is higher than the hydraulic pressure on the rod side of the locking cylinder.DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

[0025] In the following description, directions indicated by an arrow U, an arrow D, an arrow F, an arrow B, an arrow L, and an arrow R in the drawings are defined as an upward direction, a downward direction, a frontward direction, a backward direction, a leftward direction, and a rightward direction, respectively.

[0026] First, the overall configuration of a tractor 1 according to an example embodiment of the present disclosure is described.

[0027] The tractor 1 mainly includes a machine body frame 2, an engine 3, a transmission casing 4, front wheels 5, rear wheels 6, a hood 7, a cabin 8, a steering wheel 9, and a front loader 10.

[0028] The machine body frame 2 is a structure including a combination of panels. The machine body frame 2 preferably has a substantially rectangular shape in a planar view. The machine body frame 2 is positioned with a longitudinal direction of the machine body frame 2 oriented in the front-back direction. The engine 3 is fixed to a rear portion of the machine body frame 2. The transmission casing 4 is fixed to a rear portion of the engine 3. The front portion of the machine body frame 2 is supported by a pair of left and right front wheels 5 through a front axle mechanism (not shown). The rear portion of the transmission casing 4 is supported by a pair of left and right rear wheels 6 through a rear axle mechanism (not shown). The engine 3 is covered with the hood 7.

[0029] Power of the engine 3 can be transmitted to the front wheels 5 via the front axle mechanism and be transmitted to the rear wheels 6 via the rear axle mechanism, after being shifted by a transmission (not shown) housed in the transmission casing 4. The front wheels 5 and the rear wheels 6 are rotationally driven by the power of the engine 3, so that the tractor 1 can move.

[0030] The cabin 8 is provided behind the engine 3. The living space the worker occupies is provided inside the cabin 8. In the living space, the steering wheel 9 to adjust the turning angle of the front wheels 5, various operating tools, the seat on which the worker sits, and the like are provided.

[0031] The front loader 10 is attached to a front portion of the tractor 1. An attachment is detachably connected to the front loader 10. In the present example embodiment, an example in which a bucket 30 is adopted as an example of the attachment is described.

[0032] The bucket 30 shown in FIG. 1 and FIGS. 2A and 2B has a shape that is open on the front side. The bucket 30 is detachably fixed to an attachment mounting mechanism 20 (described later) of the front loader 10. As illustrated in FIGS. 2A and 2B, fixed portions 31 fixed to the attachment mounting mechanism 20 are provided on rear portions of the bucket 30. Two fixed portions 31 are provided at a distance from each other in a lateral direction. Fixed holes 31a penetrating in the lateral direction are located in the fixed portions 31.

[0033] Locking pins 23 of the attachment mounting mechanism 20 described later are inserted into the fixed holes 31a, so that the bucket 30 is fixed to the attachment mounting mechanism 20 (see FIG. 2B). Note that the mode of fixing the bucket 30 will be described later in detail. Although not described herein, in addition to the fixed portions 31, fixed portions (hook-shaped fixed portions, for example) fixed to the attachment mounting mechanism 20 may be provided on the bucket 30.

[0034] In the following, the configuration of the front loader 10 is described. The front loader 10 mainly includes frames 11, booms 12, boom cylinders 13, attachment cylinders 14, and the attachment mounting mechanism 20.

[0035] The frames 11 shown in FIG. 1 are fixed to the vehicle body of the tractor 1. The frames 11 are fixed to both the left and right sides of the vehicle body of the tractor 1. More specifically, the frames 11 are fixed to both the left sides and the right sides of the machine body frame 2 and the transmission casing 4 of the tractor 1. Although FIG. 1 illustrating the right side surface of the vehicle body of the tractor 1 shows only the right-side frame 11, a frame 11 is fixed to the left side of the vehicle body in the same manner.

[0036] The boom 12 is supported so as to be vertically rotatable with respect to upper portions of the frames 11. The booms 12 extend forward and downward from the upper portions of the pair of frames 11. The bucket 30 is vertically rotatably connected to the front end portions of the pair of booms 12 through the attachment mounting mechanism 20 described later.

[0037] The boom cylinders 13 elongate and contract to rotatably move the booms 12 with respect to the frames 11. More specifically, the boom cylinders 13 elongate to rotatably move the booms 12 upward, and contract to rock the booms 12 downward.

[0038] The boom cylinders 13 are provided for the pair of booms 12 in one-to-one correspondence. The boom cylinders 13 each include a cylinder tube and a cylinder rod. The configurations of the cylinder tubes and the cylinder rods of the boom cylinders 13 are substantially the same as the configurations of cylinder tubes 14a and cylinder rods 14b of the attachment cylinders 14 described later.

[0039] The attachment cylinders 14 elongate and contract to rock the bucket 30 connected to the front loader 10. More specifically, the attachment cylinders 14 are made to contract, so that the bucket 30 can be rocked upward. As a result, earth and sand can be scooped with the bucket 30. Also, the attachment cylinders 14 are made to elongate, so that the bucket 30 can be rocked downward. As a result, earth and sand in the bucket 30 can be unloaded (earth and sand are dumped). The attachment cylinders 14 are provided for the pair of booms 12 in one-to-one correspondence.

[0040] As illustrated in FIG. 3, the attachment cylinders 14 each include a cylinder tube 14a and a cylinder rod 14b. The cylinder tube 14a provides the housing of the attachment cylinder 14. The cylinder tube 14a preferably has a substantially cylindrical shape. Oil from an oil passage described later is fed into the cylinder tube 14a.

[0041] The cylinder rod 14b moves with respect to the cylinder tube 14a, by the hydraulic pressure in the cylinder tube 14a. The cylinder rod 14b preferably has a substantially columnar shape. On the base end side of the cylinder rod 14b (the side located inside the cylinder tube 14a), a piston 14c that has a larger diameter than the cylinder rod 14b and has a shape conforming to the inner diameter of the cylinder tube 14a is provided. The cylinder rod 14b moves with respect to the cylinder tube 14a, as the piston 14c is pushed by the hydraulic pressure in the cylinder tube 14a.

[0042] The attachment mounting mechanism 20 illustrated in FIG. 1 and FIGS. 2A and 2B can detachably fix the bucket 30. The attachment mounting mechanism 20 is switchable between a fixed state (see FIG. 2B) in which the bucket 30 is fixed, and a released state (see FIG. 2A) in which the fixing of the bucket 30 is released. The attachment mounting mechanism 20 includes attachment portions 21, a locking cylinder 22, and the locking pins 23.

[0043] The attachment portions 21 are portions to which the booms 12 and the attachment cylinders 14 are attached. The attachment portions 21 are provided on both left and right sides of the attachment mounting mechanism 20. A boom connecting hole 21a and a cylinder connecting hole 21b are located in each of the attachment portions 21.

[0044] The boom connecting hole 21a shown in FIG. 1 is a hole penetrating the attachment portion 21 in the lateral direction. A predetermined connecting shaft (not shown) is inserted into the boom connecting holes 21a. The attachment portions 21 are connected to the tip end sides of the booms 12 by the connecting shaft.

[0045] The cylinder connecting hole 21b is a hole penetrating the attachment portion 21 in the lateral direction. A predetermined connecting shaft (not shown) is inserted into the cylinder connecting holes 21b. The attachment portions 21 are connected to the tip end sides of the attachment cylinders 14 (the cylinder rods 14b) by the connecting shaft.

[0046] The locking cylinder 22 shown in FIGS. 2A and 2B elongates and contracts to operate the locking pins 23 described later. As the locking cylinder 22 is elongated and contracted, switching between the fixed state and the released state can be performed. The locking cylinder 22 is positioned with an elongating / contracting direction of the locking cylinder 22 oriented in the lateral direction. The locking cylinder 22 includes a cylinder tube 22a and a cylinder rod 22b. Note that the configurations of the cylinder tube 22a and the cylinder rod 22b are substantially the same as the configurations of cylinder tubes 14a and cylinder rods 14b of the attachment cylinders 14 described above. Therefore, explanation of the configurations of the cylinder tube 22a and the cylinder rod 22b is omitted herein. Note that a piston 22c that is substantially the same as the piston 14c described above is provided in the cylinder rod 22b. In the example illustrated in the drawings, the cylinder tube 22a is located on the left side, and the cylinder rod 22b is located on the right side.

[0047] The locking pins 23 are inserted into the fixed holes 31a of the fixed portions 31 of the bucket 30. The locking pins 23 are provided on both left and right sides of the locking cylinder 22. More specifically, the locking pins 23 are provided at the left end portion of the cylinder tube 22a and the right end portion of the cylinder rod 22b. Each of the locking pins 23 preferably has a columnar shape, with an axial direction of the locking pins 23 oriented in the elongating / contracting direction (lateral direction) of the locking cylinder 22. The tip end portion (the end portion on the side opposite to the locking cylinder 22) of each locking pin 23 preferably has a tapered shape whose diameter is smaller at a portion closer to the tip end.

[0048] Next, an operation of the attachment mounting mechanism 20 is described with reference to FIGS. 2A and 2B. Note that, in the following, the operation to be performed by the attachment mounting mechanism 20 in a case where the bucket 30 is mounted is described. FIG. 2A shows the attachment mounting mechanism 20 before the bucket 30 is mounted (the released state). In this state, the locking cylinder 22 of the attachment mounting mechanism 20 is in a contracted state.

[0049] As illustrated in FIG. 2B, in a case where the bucket 30 is mounted, the worker elongates the locking cylinder 22, to insert the respective locking pins 23 into the fixed holes 31a of the respective fixed portions 31 of the bucket 30. As a result, the attachment mounting mechanism 20 is switched to the fixed state, and the bucket 30 can be mounted onto the attachment mounting mechanism 20.

[0050] Further, as illustrated in FIG. 2A, in a case where the bucket 30 is removed, the worker makes the locking cylinder 22 contract, and pulls out each locking pin 23 from the fixed holes 31a of the respective fixed portions 31. As a result, the attachment mounting mechanism 20 is switched to the released state, and the fixing of the bucket 30 to the attachment mounting mechanism 20 can be canceled. Using an operating tool in the cabin 8, the worker can switch between the fixed state and the released state of the attachment mounting mechanism 20.

[0051] The above is the description of the configuration of the front loader 10. Using an operating tool in the cabin 8, the worker can make the boom cylinders 13 and the attachment cylinders 14 elongate and contract, to rotationally move the booms 12 of the front loader 10 and the bucket 30 as appropriate, and carry earth and sand or the like.

[0052] The front loader 10 includes a hydraulic circuit 100 that is provided to feed hydraulic oil to each of the cylinders (the boom cylinders 13, the attachment cylinders 14, and the locking cylinder 22) described above, to elongate and contract each of the cylinders.

[0053] In the following, the configuration of the hydraulic circuit 100 is described with reference to FIGS. 3 to 5B. The hydraulic circuit 100 can control the operation of each cylinder, using hydraulic oil fed from a feed source such as a predetermined tank (not shown) by a predetermined pump (not shown). Note that, in each of the drawings mentioned below, portions mainly related to operations of the attachment cylinders 14 and the locking cylinder 22 in the entire hydraulic circuit of the front loader 10 are illustrated, and portions related to operations of the other portions (the boom cylinders 13 and the like, for example) are omitted where appropriate.

[0054] The hydraulic circuit 100 includes the attachment cylinders 14, the locking cylinder 22, a switching valve 110, a feed-source-side oil passage 120, an attachment oil passage 130, a locking oil passage 140, a connecting oil passage 160, and a shut-off valve 150. Since the configurations of the attachment cylinders 14 and the locking cylinder 22 have already been described above, explanation in the description above is not made in the description below.

[0055] The switching valve 110 can switch between an “attachment-cylinder-side feeding state” in which the hydraulic oil from the feed source is fed to an oil passage (the attachment oil passage 130 described later) on the side of the attachment cylinders 14, and a “locking-cylinder-side flowing state” in which the hydraulic oil is fed to an oil passage (the locking oil passage 140 described later) on the side of the locking cylinder 22. The switching valve 110 is fed with the hydraulic oil through the feed-source-side oil passage 120 described later. The switching valve 110 can switch the oil passage by an action of solenoid or the like, for example. Note that modes of switching the oil passage with the switching valve 110 will be described later.

[0056] The switching valve 110 includes ports (a first port 111, a second port 112, a third port 113, and a fourth port 114) that are openings to which the respective oil passages (a first attachment oil passage 131, a second attachment oil passage 132, a first locking oil passage 141, and a second locking oil passage 142, which will be described later) connected to the respective cylinders are connected. The first port 111 is connected to the first attachment oil passage 131 described later. The second port 112 is connected to the first locking oil passage 141 described later. The third port 113 is connected to the second attachment oil passage 132 described later. The fourth port 114 is connected to the second locking oil passage 142 described later.

[0057] Among the respective ports, the first port 111 and the second port 112 are adjacent to each other. Also, the third port 113 and the fourth port 114 are adjacent to each other. Here, there is a possibility that the hydraulic oil flowing through the port on one side of the ports adjacent to each other leaks through the port on the other side.

[0058] The feed-source-side oil passage 120 is an oil passage that connects a device (a tank, a pump, or the like, for example) on the side of the feed source of the hydraulic oil, to the switching valve 110. The feed-source-side oil passage 120 includes a first feed-source-side oil passage 121 and a second feed-source-side oil passage 122.

[0059] Each of the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122 is connected to a port located in the switching valve 110. The hydraulic oil from the feed source side is fed into the switching valve 110 through one or both of the first feed-source-side oil passage 121 and the second feed-source-side oil passage122. Further, in a case where the hydraulic oil is fed from one of the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122, the hydraulic oil is discharged to the feed source side through the other one of the feed-source-side oil passages. Switching of the direction of flow of the hydraulic oil flowing in the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122 can be performed with a predetermined switching valve (not shown).

[0060] The attachment oil passage 130 feeds the hydraulic oil to the attachment cylinders 14, to elongate and contract the attachment cylinders 14. The attachment oil passage 130 includes a first attachment oil passage 131 and a second attachment oil passage 132.

[0061] The first attachment oil passage 131 allows the hydraulic oil for the attachment cylinders 14 to flow when the attachment cylinders 14 are made to elongate. One end portion of the first attachment oil passage 131 is connected to the first port 111 of the switching valve 110. Also, the other end portion of the first attachment oil passage 131 branches into two portions that are respectively connected to the two attachment cylinders 14. More specifically, each of the other end portions of the first attachment oil passage 131 is connected to a port on the side (bottom side) to which the hydraulic oil is fed when the attachment cylinders 14 are made to elongate, of the cylinder tube 14a of each attachment cylinder 14.

[0062] The second attachment oil passage 132 allows the hydraulic oil for the attachment cylinders 14 to flow when the attachment cylinders 14 are made to contract. One end portion of the second attachment oil passage 132 is connected to the third port 113 of the switching valve 110. Also, the other end portion of the second attachment oil passage 132 branches into two portions that are respectively connected to the two attachment cylinders 14. More specifically, each of the other end portions of the second attachment oil passage 132 is connected to a port on the side (rod side) to which the hydraulic oil is fed when the attachment cylinders 14 are made to contract, of the cylinder tube 14a of each attachment cylinder 14.

[0063] The locking oil passage 140 feeds the hydraulic oil to the locking cylinder 22, to elongate and contract the locking cylinder 22. The locking oil passage 140 includes the first locking oil passage 141 and the second locking oil passage 142.

[0064] The first locking oil passage 141 allows the hydraulic oil for the locking cylinder 22 to flow when the locking cylinder 22 is elongated. One end portion of the first locking oil passage 141 is connected to the second port 112 of the switching valve 110. Meanwhile, the other end portion of the first locking oil passage 141 is connected to a port of the cylinder tube 22a of the locking cylinder 22 on the side (bottom side) to which the hydraulic oil is fed when the locking cylinder 22 is elongated.

[0065] The hydraulic oil to be fed to the locking cylinder 22 flows in the second locking oil passage 142 when the locking cylinder 22 is made to contract. One end portion of the second locking oil passage 142 is connected to the fourth port 114 of the switching valve 110. Meanwhile, the other end portion of the second locking oil passage 142 is connected to a port of the cylinder tube 22a of the locking cylinder 22 on the side (rod side) to which the hydraulic oil is fed when the locking cylinder 22 is made to contract.

[0066] The shut-off valve 150 can restrict the flow of the hydraulic oil in the first locking oil passage 141. The shut-off valve 150 is provided in an intermediate portion of the first locking oil passage 141. Hereinafter, of the first locking oil passage 141, a portion closer to the side of the switching valve 110 (the hydraulic oil feed source side) than the shut-off valve 150 will be sometimes referred to as an “upstream oil passage 141a”, and a portion closer to the locking cylinder 22 than the shut-off valve 150 will be sometimes referred to as a “downstream oil passage 141b”.

[0067] The shut-off valve 150 is switchable between a restricting state (see FIG. 3) in which the flow of the hydraulic oil in the first locking oil passage 141 is restricted, and an allowing state (see FIG. 4) in which the flow of the hydraulic oil in the first locking oil passage 141 is allowed. In the present example embodiment, in a case where the shut-off valve 150 is in the restricting state, the flow of the hydraulic oil in the first locking oil passage 141 is restricted. Here, the state in which “the flow of the hydraulic oil is restricted” includes not only a state in which the flow of the hydraulic oil in the first locking oil passage 141 is completely restricted, but also a state in which the hydraulic oil slightly flows. The shut-off valve 150 can perform the switching by an action of a solenoid or the like, for example. In the present example embodiment, the shut-off valve 150 performs a switching operation in conjunction with the switching operation by the switching valve 110. Specifically, the shut-off valve 150 operates in conjunction with the switching valve 110 so as to be in the restricting state in a case where the switching valve 110 is in the attachment-cylinder-side feeding state, and to be in the allowing state in a case where the switching valve 110 is in the locking-cylinder-side flowing state.

[0068] The connecting oil passage 160 connects an intermediate portion of the first locking oil passage 141 and an intermediate portion of the second locking oil passage 142. As the connecting oil passage 160 is provided, the hydraulic oil is allowed to flow between the first locking oil passage 141 and the second locking oil passage 142. As illustrated in FIG. 3, the connecting oil passage 160 is connected to the upstream oil passage 141a of the first locking oil passage 141.

[0069] A throttle portion 161 to adjust the flow rate of the hydraulic oil flowing in the connecting oil passage 160 is provided in an intermediate portion of the connecting oil passage 160. As the throttle portion 161 is provided, the flow rate of the hydraulic oil flowing between the first locking oil passage 141 and the second locking oil passage 142 can be adjusted. As the throttle portion 161, a throttle valve can be used. The throttle portion 161 only needs to be able to adjust the flow rate of the hydraulic oil flowing in one direction (the direction from the second locking oil passage 142 toward the first locking oil passage 141 (the upstream oil passage 141a) in the present example embodiment) of the flowing directions of the connecting oil passage 160.

[0070] The throttle portion 161 can adjust the flow rate of the hydraulic oil in the connecting oil passage 160 so that the hydraulic oil is less likely to flow in the connecting oil passage 160 than in the first locking oil passage 141 and the second locking oil passage 142, for example. Also, the throttle portion 161 can adjust the flow rate of the hydraulic oil in the connecting oil passage 160 so that the hydraulic oil more easily flows in the connecting oil passage 160 than in the first locking oil passage 141 closed by the shut-off valve 150, for example.

[0071] The above is the description of the configuration of the hydraulic circuit 100. With the hydraulic circuit 100, operations of the attachment cylinders 14 and the locking cylinder 22 can be controlled. In the following, control on the respective cylinders using the hydraulic circuit 100 is described.

[0072] First, referring to FIGS. 3 and 4, the control to be performed when the hydraulic circuit 100 is switched between a state in which the attachment cylinders 14 are operable and a state in which the locking cylinder 22 is operable is described.

[0073] FIG. 3 illustrates the hydraulic circuit 100 in the state where the attachment cylinders 14 are operable. In this state, the switching valve 110 is in the attachment-cylinder-side feeding state, and the shut-off valve 150 is in the restricting state. In a case where the switching valve 110 is in the attachment-cylinder-side feeding state, the first port 111 and the third port 113 are opened to allow the flow of the hydraulic oil into the first attachment oil passage 131 and the second attachment oil passage 132, while the second port 112 and the fourth port 114 are closed to restrict the flow of the hydraulic oil into the first locking oil passage 141 and the second locking oil passage 142. In the state illustrated in FIG. 3, the hydraulic oil that has been fed through the feed-source-side oil passage 120 is fed to the attachment cylinders 14 in response to an operation by the worker using an operating tool in the cabin 8, and thus, the attachment cylinders 14 can be made to elongate and contract, to rock the bucket 30.

[0074] The worker can switch the hydraulic circuit 100 from the state illustrated in FIG. 3 to the state in which the locking cylinder 22 is operable as illustrated in FIG. 4, by performing an operation using an operating tool in the cabin 8. In a case where the switching operation is performed, the switching valve 110 is switched to the locking-cylinder-side flowing state, and the shut-off valve 150 is switched to the allowing state. In a case where the switching valve 110 is in the locking-cylinder-side flowing state, the second port 112 and the fourth port 114 are opened to allow the flow of the hydraulic oil into the first locking oil passage 141 and the second locking oil passage 142, while the first port 111 and the third port 113 are closed to restrict the flow of the hydraulic oil into the first attachment oil passage 131 and the second attachment oil passage 132. In the state illustrated in FIG. 4, the hydraulic oil that has been fed through the feed-source-side oil passage 120 is fed to the locking cylinder 22 in response to an operation by the worker using an operating tool in the cabin 8, and thus, the locking cylinder 22 can be made to elongate and contract, to remove the bucket 30.

[0075] Also, the worker can switch the hydraulic circuit 100 from the state illustrated in FIG. 4 to the state illustrated in FIG. 3, by performing an operation to switch the switching valve 110 to the attachment-cylinder-side feeding state and switch the shut-off valve 150 to the restricting state, using an operating tool in the cabin 8.

[0076] Next, referring to FIGS. 5A and 5B, the flow of the hydraulic oil in a case where the locking cylinder 22 is elongated and the flow of the hydraulic oil in a case where the locking cylinder 22 is contracted in the hydraulic circuit 100 in the state where the locking cylinder 22 is operable (the switching valve 110 is in the locking-cylinder-side flowing state) are described. Note that, in the example illustrated in FIGS. 5A and 5B, the direction in which the hydraulic oil flows in each oil passage is indicated by an arrow, and the portion of each oil passage in which the hydraulic pressure rises as the hydraulic oil is fed is indicated by a bold line.

[0077] Referring first to FIG. 5A, the flow of the hydraulic oil in a case where the locking cylinder 22 is elongated is described. In the case where the locking cylinder 22 is elongated, the hydraulic oil from the feed source side is fed to the switching valve 110 through both the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122. By the hydraulic oil, substantially the same hydraulic pressures are applied to the first locking oil passage 141 connected to the bottom side of the cylinder tube 22a of the locking cylinder 22, and to the second locking oil passage 142 connected to the rod side of the cylinder tube 22a.

[0078] The piston 22c of the locking cylinder 22 is subject to substantially the same hydraulic pressures from both the bottom side and the rod side of the cylinder tube 22a. Here, of the piston 22c, the area on the rod side is smaller than the area on the bottom side, because the cylinder rod 22b is provided on the rod side. Therefore, in a case where substantially the same hydraulic pressures are applied from both the bottom side and the rod side, the force acting on the piston 22c is greater on the bottom side. As the piston 22c is pushed by the bottom-side hydraulic oil, and the cylinder rod 22b moves, the locking cylinder 22 elongates.

[0079] With the above configuration, the operation of elongating the locking cylinder 22 can be performed quickly. That is, in the above configuration, in a case where a configuration in which the hydraulic oil in the first feed-source-side oil passage 121 can be merged with the hydraulic oil flowing in the second feed-source-side oil passage 122 (the hydraulic oil to be fed to the first locking oil passage 141) is adopted, when the locking cylinder 22 is elongated, the hydraulic oil discharged from the rod side of the cylinder tube 22a can be used as the hydraulic oil to be fed to the bottom side of the cylinder tube 22a. Thus, the responsiveness of the locking cylinder 22 can be enhanced.

[0080] Referring next to FIG. 5B, the flow of the hydraulic oil in a case where the locking cylinder 22 is contracted is described. In the case where the locking cylinder 22 is contracted, the hydraulic oil from the feed source side flows in the first feed-source-side oil passage 121 and is fed to the switching valve 110. The hydraulic oil flows into the second locking oil passage 142 through the fourth port 114, and is fed to the rod side of the cylinder tube 22a of the locking cylinder 22. As the piston 22c is pushed by the hydraulic oil fed to the rod side, and the cylinder rod 22b moves, the locking cylinder 22 contracts.

[0081] Further, in conjunction with the movement of the cylinder rod 22b, the hydraulic oil on the bottom side of the cylinder tube 22a is discharged from the locking cylinder 22. The discharged hydraulic oil flows into the first locking oil passage 141, and is fed to the switching valve 110 through the second port 112. The hydraulic oil flows into the second feed-source-side oil passage 122, and is returned to the feed source side.

[0082] The above is the description of flows of the hydraulic oil in cases where the locking cylinder 22 is elongated and contracted. In the hydraulic circuit 100, the throttle portion 161 is provided in the connecting oil passage 160. Accordingly, it is possible to allow the hydraulic oil to actively flow in the first locking oil passage 141 and the second locking oil passage 142, and to prevent the hydraulic oil from actively flowing in the connecting oil passage 160. Thus, it is possible to reduce the influence on operations of the locking cylinder 22 due to the connecting oil passage 160 having a flow of the hydraulic oil that is used for operations of elongating and contracting the locking cylinder 22.

[0083] Next, the flow of the hydraulic oil in the hydraulic circuit 100 in the state where the attachment cylinders 14 are operable (the switching valve 110 is in the attachment-cylinder-side feeding state) is described with reference to FIG. 3.

[0084] In a case where the attachment cylinders 14 are elongated, the hydraulic oil from the feed source side is fed to the switching valve 110 through both the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122. By the hydraulic oil, substantially the same hydraulic pressures are applied to the first attachment oil passage 131 connected to the bottom sides of the cylinder tubes 14a of the attachment cylinders 14, and to the second attachment oil passage 132 connected to the rod sides of the cylinder tubes 14a. As a result, like the locking cylinder 22 described above, the attachment cylinders 14 elongate, because of the difference between the area on the rod side and the area on the bottom side of each piston 14c. With the configuration, the responsiveness of the attachment cylinders 14 is enhanced, and the bucket 30 can quickly perform a dumping action.

[0085] Further, in a case where the attachment cylinders 14 are contracted, the hydraulic oil that has flowed from the feed source side through the first feed-source-side oil passage 121 and been fed to the switching valve 110 is then fed to the rod sides of the attachment cylinders 14 through the third port 113. As the piston 14c is pushed by the fed hydraulic oil, and the cylinder rods 14b move, the attachment cylinders 14 contract. Further, in conjunction with the movement of the cylinder rods 14b, the hydraulic oil discharged from the bottom sides of the cylinder tubes 14a flows through the first attachment oil passage 131, and is fed to the switching valve 110 through the first port 111. The hydraulic oil flows into the second feed-source-side oil passage 122, and is returned to the feed source side.

[0086] In the above manner, the worker can elongate and contract the attachment cylinders 14, using the hydraulic circuit 100 according to the present example embodiment. As described above, in the hydraulic circuit 100 according to the present example embodiment, the oil passages (the first attachment oil passage 131 and the second attachment oil passage 132) on the side of the attachment cylinders 14, and the oil passages (the first locking oil passage 141 and the second locking oil passage 142) on the side of the locking cylinder 22 are connected to the respective ports of the common switching valve 110. That is, the oil passages on the side of the attachment cylinder 14 and the oil passages on the side of the locking cylinder 22 are indirectly connected through the common switching valve 110. On the other hand, the oil passages on the side of the attachment cylinders 14 and the oil passages on the side of the locking cylinder 22 are not connected by some other oil passage or the like.

[0087] In the hydraulic circuit 100 as described above, there is a possibility that the hydraulic oil will unintentionally flow from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22 due to leakage of the hydraulic oil at the switching valve 110.

[0088] In the following, a flow of hydraulic oil leaking through the switching valve 110 is described, with reference to a conventional hydraulic circuit 40 illustrated in FIG. 6. Note that the hydraulic circuit 40 has substantially the same configuration as the hydraulic circuit 100, except that the connecting oil passage 160 is not provided therein. Therefore, in the following, the hydraulic circuit 40 having components denoted by the same reference signs as those in the hydraulic circuit 100 is used in the description.

[0089] FIG. 6 illustrates an example in which the attachment cylinders 14 are contracted in the hydraulic circuit 40 in a state where the attachment cylinders 14 are operable. In this case, the hydraulic oil that has flowed from the feed source side through the first feed-source-side oil passage 121 and been fed to the switching valve 110 is then fed to the rod sides of the attachment cylinders 14 through the third port 113.

[0090] Here, the third port 113 and the fourth port 114 of the switching valve 110 are adjacent to each other. Therefore, the hydraulic oil flowing through the third port 113 leaks through the adjacent fourth port 114 to flow into the second locking oil passage 142 in some cases. In such a case, a force is applied to the locking cylinder 22 in a contracting direction by the hydraulic oil fed to the rod side through the second locking oil passage 142. In this case, in conjunction with the movement of the cylinder rod 22b, the hydraulic oil on the bottom side of the locking cylinder 22 flows into the downstream oil passage 141b of the first locking oil passage 141, and the hydraulic pressure in the downstream oil passage 141b becomes higher than the hydraulic pressure in the upstream oil passage 141a.

[0091] In this state, the hydraulic oil easily flows from the downstream oil passage 141b into the upstream oil passage 141a. Although the shut-off valve 150 is provided between the downstream oil passage 141b and the upstream oil passage 141a, even in a case where the shut-off valve 150 is provided, the hydraulic oil slightly passes through the shut-off valve 150, and the hydraulic oil on the bottom side of the locking cylinder 22 easily leaks to the side of the switching valve 110. As a result, in the hydraulic circuit 40, the locking cylinder 22 might unintentionally contract.

[0092] In the hydraulic circuit 100 according to the present example embodiment, on the other hand, even in a case where the hydraulic oil flows from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22 due to leakage through the switching valve 110, contraction of the locking cylinder 22 is prevented.

[0093] In the following, flows of the hydraulic oil in an oil passage on the side of the locking cylinder 22 in the hydraulic circuit 100 in the state where the attachment cylinders 14 are operable are described with reference to FIGS. 7A and 7B. FIGS. 7A and 7B each illustrate an example in which the hydraulic oil flows from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22 (the second locking oil passage 142) due to leakage from the third port 113 to the fourth port 114 of the switching valve 110. Note that, in the description below, flows of the hydraulic oil in the oil passages on the side of the attachment cylinder 14 are not explained.

[0094] As illustrated in FIG. 7A, in a case where the hydraulic oil flows into the second locking oil passage 142 in conjunction with the leakage of the hydraulic oil, the hydraulic pressure on the rod side of the locking cylinder 22 (the hydraulic pressure in the second locking oil passage 142) becomes higher than the hydraulic pressure on the bottom side (the hydraulic pressure in the downstream oil passage 141b of the first locking oil passage 141). Here, in the hydraulic circuit 100, the second locking oil passage 142 and the upstream oil passage 141a of the first locking oil passage 141 are connected by the connecting oil passage 160. Therefore, in the hydraulic circuit 100, the hydraulic oil from the second locking oil passage 142 flows into the upstream oil passage 141a through the connecting oil passage 160, and the hydraulic pressures in the second locking oil passage 142 and the upstream oil passage 141a become substantially equal. In this case, the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 is higher than the hydraulic pressure in the downstream oil passage 141b.

[0095] As described above, in a case where the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 is made higher than the hydraulic pressure in the downstream oil passage 141b, it is possible to prevent the hydraulic oil on the bottom side of the locking cylinder 22 from leaking to the side of the switching valve 110 through the first locking oil passage 141. Thus, contraction of the locking cylinder 22 is prevented, and unintended detachment of the bucket 30 from the attachment mounting mechanism 20 is prevented.

[0096] FIG. 7B illustrates a state in which the hydraulic pressure on the bottom side of the locking cylinder 22 (the hydraulic pressure in the downstream oil passage 141b of the first locking oil passage 141) is higher than the hydraulic pressure on the rod side (the hydraulic pressure in the second locking oil passage 142). In this case, the hydraulic oil in the downstream oil passage 141b of the first locking oil passage 141 having a relatively high hydraulic pressure slightly flows into the upstream oil passage 141a through the shut-off valve 150. As a result, the locking cylinder 22 slightly contracts.

[0097] As the hydraulic oil flows, the hydraulic pressure in the downstream oil passage 141b of the first locking oil passage 141 gradually drops. Along with this, the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 and the hydraulic pressure in the second locking oil passage 142 connected to the upstream oil passage 141a through the connecting oil passage 160 both rise.

[0098] At the time when the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 becomes equal to or higher than the hydraulic pressure in the downstream oil passage 141b, the flow of the hydraulic oil from the downstream oil passage 141b into the upstream oil passage 141a stops. Accordingly, the locking cylinder 22 does not contract any more. In a case where the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 becomes higher than the hydraulic pressure in the downstream oil passage 141b, the hydraulic circuit 100 is in a state that is substantially the same as the state illustrated in FIG. 7A. With the configuration, contraction of the locking cylinder 22 is prevented, and unintended detachment of the bucket 30 from the attachment mounting mechanism 20 is prevented.

[0099] As described above, in the hydraulic circuit 100 according to the present example embodiment, it is possible to prevent unintended contraction of the locking cylinder 22, regardless of the state of the hydraulic pressure in the locking cylinder 22 (a state in which the hydraulic pressure on bottom side is high, or a state in which the hydraulic pressure on the rod side is high).

[0100] Also, in the hydraulic circuit 100 according to the present example embodiment, the connecting oil passage 160 is connected not to the downstream oil passage 141b of the first locking oil passage 141, but to the upstream oil passage 141a, and thus, unintended elongation of the locking cylinder 22 is prevented. That is, in a case where the connecting oil passage 160 is connected to the downstream oil passage 141b, there is a possibility that the hydraulic oil in the downstream oil passage 141b will be fed directly to the bottom side of the locking cylinder 22, as the hydraulic oil flows from an oil passage on the side of the attachment cylinder 14 into an oil passage on the side of the locking cylinder 22 due to leakage at the switching valve 110. Because of this, there is a possibility that the locking cylinder 22 will unintentionally elongate.

[0101] On the other hand, in a case where the connecting oil passage 160 is connected to the upstream oil passage 141a of the first locking oil passage 141 as in the hydraulic circuit 100 according to the present example embodiment, the shut-off valve 150 limits the flow rate of the hydraulic oil from the upstream oil passage 141a into the downstream oil passage 141b. Thus, unintended elongation of the locking cylinder 22 is prevented.

[0102] As described above, the hydraulic circuit 100 according to the present example embodiment includes the locking cylinder 22 to elongate and contract to switch between a fixed state in which the bucket 30 (an attachment) is fixed to the front loader 10 (a loader) and a released state in which fixing of the bucket 30 to the front loader 10 is canceled, the first locking oil passage 141 through which the hydraulic oil to be fed to the locking cylinder 22 flows to put the locking cylinder 22 into the fixed state, the second locking oil passage 142 through which the hydraulic oil to be fed to the locking cylinder 22 flows to put the locking cylinder 22 into the released state, and the connecting oil passage 160 that connects the first locking oil passage 141 and the second locking oil passage 142 and includes a throttle portion 161 to adjust the flow rate of the hydraulic oil flowing between the first locking oil passage 141 and the second locking oil passage 142.

[0103] With such a configuration, unintended detachment of the bucket 30 is prevented. Specifically, in a conventional hydraulic circuit, in a case where hydraulic oil leaking from some other portion (an attachment cylinder 14 or the like, for example) is fed to the second locking oil passage 142, the hydraulic pressure in the second locking oil passage 142 might become higher than the hydraulic pressure in the first locking oil passage 141. In this case, the hydraulic oil in the locking cylinder 22 leaks through the first locking oil passage 141. As a result, the locking cylinder 22 might unintentionally contract, and the attachment might be easily detached. On the other hand, the first locking oil passage 141 and the second locking oil passage 142 are connected through the connecting oil passage 160 as in the hydraulic circuit 100 according to the present example embodiment, so that the first locking oil passage 141 and the second locking oil passage 142 are kept at equal or substantially equal pressures. Thus, leakage of the hydraulic oil in the locking cylinder 22 through the first locking oil passage 141 is prevented, and contraction of the locking cylinder 22 is prevented. Also, as the throttle portion 161 is provided in the connecting oil passage160, an active flow of the hydraulic oil in the connecting oil passage 160 is prevented when the locking cylinder 22 is intentionally operated. Thus, the influence on the operation of the locking cylinder 22 is reduced.

[0104] Further, the hydraulic circuit 100 includes the shut-off valve 150 to restrict the flow of the hydraulic oil in the first locking oil passage 141, and the connecting oil passage 160 is connected to the side of the feed source of the hydraulic oil with respect to the shut-off valve 150 in the first locking oil passage 141.

[0105] With such a configuration, unintended elongation of the locking cylinder 22 is prevented. Specifically, as the connecting oil passage 160 is connected to the first locking oil passage 141 at a portion closer to the feed source than the shut-off valve 150, the amount of feed of the hydraulic oil to the locking cylinder 22 can be limited in a case where the hydraulic oil leaking from some other portion (an attachment cylinder 14 or the like, for example) in the hydraulic circuit 100 is supplied to the first locking oil passage 141 through the connecting oil passage 160. Thus, unintended elongation of the locking cylinder 22 is prevented.

[0106] Further, the hydraulic circuit 100 includes the switching valve 110 to switch between a state in which the hydraulic oil from the feed source is fed to the side of the locking cylinder 22, and a state in which the hydraulic oil is fed to the side of another cylinder different from the locking cylinder 22, and another oil passage through which the hydraulic oil to be fed from the switching valve 110 to the another cylinder flows, and the first locking oil passage 141, the second locking oil passage 142, and the another oil passage are each connected to the switching valve110.

[0107] With such a configuration, it is possible to prevent unintended contraction of the locking cylinder 22 due to the hydraulic oil leaking from another oil passage through the switching valve 110.

[0108] Further, a front loader 10 (a loader) according to an example embodiment includes the hydraulic circuit 100 according to the present example embodiment.

[0109] With such a configuration, unintended detachment of the bucket 30 is prevented.

[0110] Furthermore, a tractor 1 (a working machine) according to an example embodiment includes the front loader 10 according to the present example embodiment.

[0111] With such a configuration, unintended detachment of the bucket 30 is prevented.

[0112] Note that the tractor 1 according to the present example embodiment is an example embodiment of a working machine according to the present disclosure.

[0113] Also, the front loader 10 according to the present example embodiment is an example embodiment of a loader according to the present disclosure.

[0114] Further, the bucket 30 according to the present example embodiment is an example embodiment of an attachment according to the present disclosure.

[0115] Although some example embodiments of the present disclosure have been described so far, the present disclosure is not limited to the above configurations, and various modifications can be made to it within the scope of the present invention.

[0116] For example, the shape of each of the structural elements (the front loader 10, the bucket 30, and the like), the configuration of the hydraulic circuit 100, and the like described in the above example embodiments are merely examples, and are not limited to the example embodiments described above.

[0117] Specifically, in the hydraulic circuits 100 according to the present example embodiments, when the respective cylinders (the attachment cylinders 14 and the locking cylinder 22) are elongated, the hydraulic oil is fed to both the bottom side and the rod side of each cylinder, and each cylinder is elongated by taking advantage of the difference in area of each piston. However, the present disclosure is not limited to this. For example, it is also possible to adopt a configuration in which the hydraulic oil is fed only to the rod side, and the hydraulic oil on the bottom side is discharged from each cylinder when each cylinder is elongated.

[0118] Also, in the examples described in the above example embodiments, the connecting oil passage 160 is connected to the upstream oil passage 141a of the first locking oil passage 141. However, the present disclosure is not limited to this. For example, the connecting oil passage 160 can be connected to the downstream oil passage 141b. In this case, even if the hydraulic oil leaks from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22, the areas of the piston 22c of the locking cylinder 22 on the bottom side and the rod side can be set as appropriate to prevent unintended elongation of the locking cylinder 22.

[0119] Further, in the above example embodiments, the bucket 30 has been described as an example of the attachment. However, the attachment is not limited to this configuration. As the attachment, various kinds of attachments (a roll grab, a fork, and the like, for example) that can be attached to the front loader 10 can be adopted, instead of or in addition to the bucket 30, for example.

[0120] Also, in the examples described in the above example embodiment, the tractor 1 has been described as an example of the working machine. However, the working machine is not limited to such a machine. For example, a working machine may be some other agricultural vehicle, a construction vehicle, an industrial vehicle, or the like.

[0121] While example embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Examples

Embodiment Construction

[0025]In the following description, directions indicated by an arrow U, an arrow D, an arrow F, an arrow B, an arrow L, and an arrow R in the drawings are defined as an upward direction, a downward direction, a frontward direction, a backward direction, a leftward direction, and a rightward direction, respectively.

[0026]First, the overall configuration of a tractor 1 according to an example embodiment of the present disclosure is described.

[0027]The tractor 1 mainly includes a machine body frame 2, an engine 3, a transmission casing 4, front wheels 5, rear wheels 6, a hood 7, a cabin 8, a steering wheel 9, and a front loader 10.

[0028]The machine body frame 2 is a structure including a combination of panels. The machine body frame 2 preferably has a substantially rectangular shape in a planar view. The machine body frame 2 is positioned with a longitudinal direction of the machine body frame 2 oriented in the front-back direction. The engine 3 is fixed to a rear portion of the machin...

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to Japanese Patent Application No. 2025-054725 filed on Mar. 28, 2025. The entire contents of this application are hereby incorporated herein by reference.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present disclosure relates to hydraulic circuits, loaders, and working machines.2. Description of the Related Art

[0003] Conventionally, a technique for working machines each including a loader to which an attachment can be detachably attached is known. As the loader, there is one to which an attachment can be detachably attached, with a cylinder being elongated and contracted by hydraulic pressure. For example, JP 2024-126696 A discloses such a configuration.

[0004] JP 2024-126696 A discloses a working vehicle that includes a working device (a loader) having a bucket as an attachment. In the working vehicle, the bucket is attached to the working device through a quick hitch provided at the tip end of an arm of the working device. The quick hitch includes a quick cylinder that elongates and contracts by hydraulic pressure of hydraulic oil. In the working vehicle, the quick cylinder is elongated to lock the quick hitch with respect to the bucket, and the quick cylinder is contracted to release the lock of the quick hitch with respect to the bucket.

[0005] Here, with the quick hitch disclosed in JP 2024-126696 A, there is a possibility that the quick cylinder will contract in a case where the hydraulic oil leaks from a valve. In this case, there is a possibility that the lock of the quick hitch will be unintentionally released, and the bucket will be detached from the quick hitch.SUMMARY OF THE INVENTION

[0006] Example embodiments of the present disclosure provide hydraulic circuits, loaders, and working machines each capable of preventing unintended detachment of an attachment.

[0007] A hydraulic circuit according to an example embodiment of the present disclosure includes a locking cylinder to elongate and contract to switch between a fixed state in which an attachment is fixed to a loader and a released state in which fixing of the attachment to the loader is canceled, a first locking oil passage through which hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the fixed state, a second locking oil passage through which the hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the released state, and a connecting oil passage that connects the first locking oil passage and the second locking oil passage, and includes a throttle portion to adjust a flow rate of the hydraulic oil flowing between the first locking oil passage and the second locking oil passage.

[0008] According to an example embodiment of the present disclosure, unintended detachment of the attachment is prevented.

[0009] A hydraulic circuit according to an example embodiment of the present disclosure further includes a shut-off valve to restrict flowing of the hydraulic oil in the first locking oil passage, and the connecting oil passage is connected to the side of the feed source of the hydraulic oil with respect to the shut-off valve in the first locking oil passage.

[0010] According to an example embodiment of the present disclosure, unintended elongation of the locking cylinder is prevented.

[0011] A hydraulic circuit according to an example embodiment of the present disclosure further includes a switching valve to switch between a state in which the hydraulic oil from the feed source is fed to the side of the locking cylinder, and a state in which the hydraulic oil is fed to the side of another cylinder different from the locking cylinder, and another oil passage through which the hydraulic oil to be fed from the switching valve to the another cylinder flows. In the hydraulic circuit, the first locking oil passage, the second locking oil passage, and the another oil passage are each connected to the switching valve.

[0012] According to an example embodiment of the present disclosure, it is possible to prevent unintended contraction of the locking cylinder due to the hydraulic oil leaking from another oil passage through the switching valve.

[0013] A loader according to an example embodiment of the present disclosure includes the hydraulic circuit according to an example embodiment of the present disclosure.

[0014] According to an example embodiment of the present disclosure, unintended detachment of the attachment is prevented.

[0015] A working machine according to an example embodiment of the present disclosure includes a loader according to an example embodiment of the present disclosure.

[0016] According to example embodiments of the present disclosure, unintended detachment of the attachment is prevented.

[0017] The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a side view showing the overall configuration of a tractor according to an example embodiment of the present disclosure.

[0019] FIG. 2A is a plan view schematically illustrating an attachment mounting mechanism and a bucket in a released state, and FIG. 2B is a plan view schematically illustrating the attachment mounting mechanism and the bucket in a fixed state.

[0020] FIG. 3 is an explanatory diagram illustrating a hydraulic circuit in a state where attachment cylinders are operable.

[0021] FIG. 4 is an explanatory diagram illustrating the hydraulic circuit in a state where a locking cylinder is operable.

[0022] FIG. 5A is an explanatory diagram illustrating the flow of hydraulic oil in a case where the locking cylinder is elongated, and FIG. 5B is an explanatory diagram illustrating the flow of hydraulic oil in a case where the locking cylinder is made to contract.

[0023] FIG. 6 is an explanatory diagram illustrating an example of a conventional hydraulic circuit.

[0024] FIG. 7A is an explanatory diagram illustrating a state in which the attachment cylinders are operable, and the hydraulic pressure on the rod side is higher than the hydraulic pressure on the bottom side of the locking cylinder, and FIG. 7B is an explanatory diagram illustrating a state in which the attachment cylinders are operable, and the hydraulic pressure on the bottom side is higher than the hydraulic pressure on the rod side of the locking cylinder.DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS

[0025] In the following description, directions indicated by an arrow U, an arrow D, an arrow F, an arrow B, an arrow L, and an arrow R in the drawings are defined as an upward direction, a downward direction, a frontward direction, a backward direction, a leftward direction, and a rightward direction, respectively.

[0026] First, the overall configuration of a tractor 1 according to an example embodiment of the present disclosure is described.

[0027] The tractor 1 mainly includes a machine body frame 2, an engine 3, a transmission casing 4, front wheels 5, rear wheels 6, a hood 7, a cabin 8, a steering wheel 9, and a front loader 10.

[0028] The machine body frame 2 is a structure including a combination of panels. The machine body frame 2 preferably has a substantially rectangular shape in a planar view. The machine body frame 2 is positioned with a longitudinal direction of the machine body frame 2 oriented in the front-back direction. The engine 3 is fixed to a rear portion of the machine body frame 2. The transmission casing 4 is fixed to a rear portion of the engine 3. The front portion of the machine body frame 2 is supported by a pair of left and right front wheels 5 through a front axle mechanism (not shown). The rear portion of the transmission casing 4 is supported by a pair of left and right rear wheels 6 through a rear axle mechanism (not shown). The engine 3 is covered with the hood 7.

[0029] Power of the engine 3 can be transmitted to the front wheels 5 via the front axle mechanism and be transmitted to the rear wheels 6 via the rear axle mechanism, after being shifted by a transmission (not shown) housed in the transmission casing 4. The front wheels 5 and the rear wheels 6 are rotationally driven by the power of the engine 3, so that the tractor 1 can move.

[0030] The cabin 8 is provided behind the engine 3. The living space the worker occupies is provided inside the cabin 8. In the living space, the steering wheel 9 to adjust the turning angle of the front wheels 5, various operating tools, the seat on which the worker sits, and the like are provided.

[0031] The front loader 10 is attached to a front portion of the tractor 1. An attachment is detachably connected to the front loader 10. In the present example embodiment, an example in which a bucket 30 is adopted as an example of the attachment is described.

[0032] The bucket 30 shown in FIG. 1 and FIGS. 2A and 2B has a shape that is open on the front side. The bucket 30 is detachably fixed to an attachment mounting mechanism 20 (described later) of the front loader 10. As illustrated in FIGS. 2A and 2B, fixed portions 31 fixed to the attachment mounting mechanism 20 are provided on rear portions of the bucket 30. Two fixed portions 31 are provided at a distance from each other in a lateral direction. Fixed holes 31a penetrating in the lateral direction are located in the fixed portions 31.

[0033] Locking pins 23 of the attachment mounting mechanism 20 described later are inserted into the fixed holes 31a, so that the bucket 30 is fixed to the attachment mounting mechanism 20 (see FIG. 2B). Note that the mode of fixing the bucket 30 will be described later in detail. Although not described herein, in addition to the fixed portions 31, fixed portions (hook-shaped fixed portions, for example) fixed to the attachment mounting mechanism 20 may be provided on the bucket 30.

[0034] In the following, the configuration of the front loader 10 is described. The front loader 10 mainly includes frames 11, booms 12, boom cylinders 13, attachment cylinders 14, and the attachment mounting mechanism 20.

[0035] The frames 11 shown in FIG. 1 are fixed to the vehicle body of the tractor 1. The frames 11 are fixed to both the left and right sides of the vehicle body of the tractor 1. More specifically, the frames 11 are fixed to both the left sides and the right sides of the machine body frame 2 and the transmission casing 4 of the tractor 1. Although FIG. 1 illustrating the right side surface of the vehicle body of the tractor 1 shows only the right-side frame 11, a frame 11 is fixed to the left side of the vehicle body in the same manner.

[0036] The boom 12 is supported so as to be vertically rotatable with respect to upper portions of the frames 11. The booms 12 extend forward and downward from the upper portions of the pair of frames 11. The bucket 30 is vertically rotatably connected to the front end portions of the pair of booms 12 through the attachment mounting mechanism 20 described later.

[0037] The boom cylinders 13 elongate and contract to rotatably move the booms 12 with respect to the frames 11. More specifically, the boom cylinders 13 elongate to rotatably move the booms 12 upward, and contract to rock the booms 12 downward.

[0038] The boom cylinders 13 are provided for the pair of booms 12 in one-to-one correspondence. The boom cylinders 13 each include a cylinder tube and a cylinder rod. The configurations of the cylinder tubes and the cylinder rods of the boom cylinders 13 are substantially the same as the configurations of cylinder tubes 14a and cylinder rods 14b of the attachment cylinders 14 described later.

[0039] The attachment cylinders 14 elongate and contract to rock the bucket 30 connected to the front loader 10. More specifically, the attachment cylinders 14 are made to contract, so that the bucket 30 can be rocked upward. As a result, earth and sand can be scooped with the bucket 30. Also, the attachment cylinders 14 are made to elongate, so that the bucket 30 can be rocked downward. As a result, earth and sand in the bucket 30 can be unloaded (earth and sand are dumped). The attachment cylinders 14 are provided for the pair of booms 12 in one-to-one correspondence.

[0040] As illustrated in FIG. 3, the attachment cylinders 14 each include a cylinder tube 14a and a cylinder rod 14b. The cylinder tube 14a provides the housing of the attachment cylinder 14. The cylinder tube 14a preferably has a substantially cylindrical shape. Oil from an oil passage described later is fed into the cylinder tube 14a.

[0041] The cylinder rod 14b moves with respect to the cylinder tube 14a, by the hydraulic pressure in the cylinder tube 14a. The cylinder rod 14b preferably has a substantially columnar shape. On the base end side of the cylinder rod 14b (the side located inside the cylinder tube 14a), a piston 14c that has a larger diameter than the cylinder rod 14b and has a shape conforming to the inner diameter of the cylinder tube 14a is provided. The cylinder rod 14b moves with respect to the cylinder tube 14a, as the piston 14c is pushed by the hydraulic pressure in the cylinder tube 14a.

[0042] The attachment mounting mechanism 20 illustrated in FIG. 1 and FIGS. 2A and 2B can detachably fix the bucket 30. The attachment mounting mechanism 20 is switchable between a fixed state (see FIG. 2B) in which the bucket 30 is fixed, and a released state (see FIG. 2A) in which the fixing of the bucket 30 is released. The attachment mounting mechanism 20 includes attachment portions 21, a locking cylinder 22, and the locking pins 23.

[0043] The attachment portions 21 are portions to which the booms 12 and the attachment cylinders 14 are attached. The attachment portions 21 are provided on both left and right sides of the attachment mounting mechanism 20. A boom connecting hole 21a and a cylinder connecting hole 21b are located in each of the attachment portions 21.

[0044] The boom connecting hole 21a shown in FIG. 1 is a hole penetrating the attachment portion 21 in the lateral direction. A predetermined connecting shaft (not shown) is inserted into the boom connecting holes 21a. The attachment portions 21 are connected to the tip end sides of the booms 12 by the connecting shaft.

[0045] The cylinder connecting hole 21b is a hole penetrating the attachment portion 21 in the lateral direction. A predetermined connecting shaft (not shown) is inserted into the cylinder connecting holes 21b. The attachment portions 21 are connected to the tip end sides of the attachment cylinders 14 (the cylinder rods 14b) by the connecting shaft.

[0046] The locking cylinder 22 shown in FIGS. 2A and 2B elongates and contracts to operate the locking pins 23 described later. As the locking cylinder 22 is elongated and contracted, switching between the fixed state and the released state can be performed. The locking cylinder 22 is positioned with an elongating / contracting direction of the locking cylinder 22 oriented in the lateral direction. The locking cylinder 22 includes a cylinder tube 22a and a cylinder rod 22b. Note that the configurations of the cylinder tube 22a and the cylinder rod 22b are substantially the same as the configurations of cylinder tubes 14a and cylinder rods 14b of the attachment cylinders 14 described above. Therefore, explanation of the configurations of the cylinder tube 22a and the cylinder rod 22b is omitted herein. Note that a piston 22c that is substantially the same as the piston 14c described above is provided in the cylinder rod 22b. In the example illustrated in the drawings, the cylinder tube 22a is located on the left side, and the cylinder rod 22b is located on the right side.

[0047] The locking pins 23 are inserted into the fixed holes 31a of the fixed portions 31 of the bucket 30. The locking pins 23 are provided on both left and right sides of the locking cylinder 22. More specifically, the locking pins 23 are provided at the left end portion of the cylinder tube 22a and the right end portion of the cylinder rod 22b. Each of the locking pins 23 preferably has a columnar shape, with an axial direction of the locking pins 23 oriented in the elongating / contracting direction (lateral direction) of the locking cylinder 22. The tip end portion (the end portion on the side opposite to the locking cylinder 22) of each locking pin 23 preferably has a tapered shape whose diameter is smaller at a portion closer to the tip end.

[0048] Next, an operation of the attachment mounting mechanism 20 is described with reference to FIGS. 2A and 2B. Note that, in the following, the operation to be performed by the attachment mounting mechanism 20 in a case where the bucket 30 is mounted is described. FIG. 2A shows the attachment mounting mechanism 20 before the bucket 30 is mounted (the released state). In this state, the locking cylinder 22 of the attachment mounting mechanism 20 is in a contracted state.

[0049] As illustrated in FIG. 2B, in a case where the bucket 30 is mounted, the worker elongates the locking cylinder 22, to insert the respective locking pins 23 into the fixed holes 31a of the respective fixed portions 31 of the bucket 30. As a result, the attachment mounting mechanism 20 is switched to the fixed state, and the bucket 30 can be mounted onto the attachment mounting mechanism 20.

[0050] Further, as illustrated in FIG. 2A, in a case where the bucket 30 is removed, the worker makes the locking cylinder 22 contract, and pulls out each locking pin 23 from the fixed holes 31a of the respective fixed portions 31. As a result, the attachment mounting mechanism 20 is switched to the released state, and the fixing of the bucket 30 to the attachment mounting mechanism 20 can be canceled. Using an operating tool in the cabin 8, the worker can switch between the fixed state and the released state of the attachment mounting mechanism 20.

[0051] The above is the description of the configuration of the front loader 10. Using an operating tool in the cabin 8, the worker can make the boom cylinders 13 and the attachment cylinders 14 elongate and contract, to rotationally move the booms 12 of the front loader 10 and the bucket 30 as appropriate, and carry earth and sand or the like.

[0052] The front loader 10 includes a hydraulic circuit 100 that is provided to feed hydraulic oil to each of the cylinders (the boom cylinders 13, the attachment cylinders 14, and the locking cylinder 22) described above, to elongate and contract each of the cylinders.

[0053] In the following, the configuration of the hydraulic circuit 100 is described with reference to FIGS. 3 to 5B. The hydraulic circuit 100 can control the operation of each cylinder, using hydraulic oil fed from a feed source such as a predetermined tank (not shown) by a predetermined pump (not shown). Note that, in each of the drawings mentioned below, portions mainly related to operations of the attachment cylinders 14 and the locking cylinder 22 in the entire hydraulic circuit of the front loader 10 are illustrated, and portions related to operations of the other portions (the boom cylinders 13 and the like, for example) are omitted where appropriate.

[0054] The hydraulic circuit 100 includes the attachment cylinders 14, the locking cylinder 22, a switching valve 110, a feed-source-side oil passage 120, an attachment oil passage 130, a locking oil passage 140, a connecting oil passage 160, and a shut-off valve 150. Since the configurations of the attachment cylinders 14 and the locking cylinder 22 have already been described above, explanation in the description above is not made in the description below.

[0055] The switching valve 110 can switch between an “attachment-cylinder-side feeding state” in which the hydraulic oil from the feed source is fed to an oil passage (the attachment oil passage 130 described later) on the side of the attachment cylinders 14, and a “locking-cylinder-side flowing state” in which the hydraulic oil is fed to an oil passage (the locking oil passage 140 described later) on the side of the locking cylinder 22. The switching valve 110 is fed with the hydraulic oil through the feed-source-side oil passage 120 described later. The switching valve 110 can switch the oil passage by an action of solenoid or the like, for example. Note that modes of switching the oil passage with the switching valve 110 will be described later.

[0056] The switching valve 110 includes ports (a first port 111, a second port 112, a third port 113, and a fourth port 114) that are openings to which the respective oil passages (a first attachment oil passage 131, a second attachment oil passage 132, a first locking oil passage 141, and a second locking oil passage 142, which will be described later) connected to the respective cylinders are connected. The first port 111 is connected to the first attachment oil passage 131 described later. The second port 112 is connected to the first locking oil passage 141 described later. The third port 113 is connected to the second attachment oil passage 132 described later. The fourth port 114 is connected to the second locking oil passage 142 described later.

[0057] Among the respective ports, the first port 111 and the second port 112 are adjacent to each other. Also, the third port 113 and the fourth port 114 are adjacent to each other. Here, there is a possibility that the hydraulic oil flowing through the port on one side of the ports adjacent to each other leaks through the port on the other side.

[0058] The feed-source-side oil passage 120 is an oil passage that connects a device (a tank, a pump, or the like, for example) on the side of the feed source of the hydraulic oil, to the switching valve 110. The feed-source-side oil passage 120 includes a first feed-source-side oil passage 121 and a second feed-source-side oil passage 122.

[0059] Each of the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122 is connected to a port located in the switching valve 110. The hydraulic oil from the feed source side is fed into the switching valve 110 through one or both of the first feed-source-side oil passage 121 and the second feed-source-side oil passage122. Further, in a case where the hydraulic oil is fed from one of the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122, the hydraulic oil is discharged to the feed source side through the other one of the feed-source-side oil passages. Switching of the direction of flow of the hydraulic oil flowing in the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122 can be performed with a predetermined switching valve (not shown).

[0060] The attachment oil passage 130 feeds the hydraulic oil to the attachment cylinders 14, to elongate and contract the attachment cylinders 14. The attachment oil passage 130 includes a first attachment oil passage 131 and a second attachment oil passage 132.

[0061] The first attachment oil passage 131 allows the hydraulic oil for the attachment cylinders 14 to flow when the attachment cylinders 14 are made to elongate. One end portion of the first attachment oil passage 131 is connected to the first port 111 of the switching valve 110. Also, the other end portion of the first attachment oil passage 131 branches into two portions that are respectively connected to the two attachment cylinders 14. More specifically, each of the other end portions of the first attachment oil passage 131 is connected to a port on the side (bottom side) to which the hydraulic oil is fed when the attachment cylinders 14 are made to elongate, of the cylinder tube 14a of each attachment cylinder 14.

[0062] The second attachment oil passage 132 allows the hydraulic oil for the attachment cylinders 14 to flow when the attachment cylinders 14 are made to contract. One end portion of the second attachment oil passage 132 is connected to the third port 113 of the switching valve 110. Also, the other end portion of the second attachment oil passage 132 branches into two portions that are respectively connected to the two attachment cylinders 14. More specifically, each of the other end portions of the second attachment oil passage 132 is connected to a port on the side (rod side) to which the hydraulic oil is fed when the attachment cylinders 14 are made to contract, of the cylinder tube 14a of each attachment cylinder 14.

[0063] The locking oil passage 140 feeds the hydraulic oil to the locking cylinder 22, to elongate and contract the locking cylinder 22. The locking oil passage 140 includes the first locking oil passage 141 and the second locking oil passage 142.

[0064] The first locking oil passage 141 allows the hydraulic oil for the locking cylinder 22 to flow when the locking cylinder 22 is elongated. One end portion of the first locking oil passage 141 is connected to the second port 112 of the switching valve 110. Meanwhile, the other end portion of the first locking oil passage 141 is connected to a port of the cylinder tube 22a of the locking cylinder 22 on the side (bottom side) to which the hydraulic oil is fed when the locking cylinder 22 is elongated.

[0065] The hydraulic oil to be fed to the locking cylinder 22 flows in the second locking oil passage 142 when the locking cylinder 22 is made to contract. One end portion of the second locking oil passage 142 is connected to the fourth port 114 of the switching valve 110. Meanwhile, the other end portion of the second locking oil passage 142 is connected to a port of the cylinder tube 22a of the locking cylinder 22 on the side (rod side) to which the hydraulic oil is fed when the locking cylinder 22 is made to contract.

[0066] The shut-off valve 150 can restrict the flow of the hydraulic oil in the first locking oil passage 141. The shut-off valve 150 is provided in an intermediate portion of the first locking oil passage 141. Hereinafter, of the first locking oil passage 141, a portion closer to the side of the switching valve 110 (the hydraulic oil feed source side) than the shut-off valve 150 will be sometimes referred to as an “upstream oil passage 141a”, and a portion closer to the locking cylinder 22 than the shut-off valve 150 will be sometimes referred to as a “downstream oil passage 141b”.

[0067] The shut-off valve 150 is switchable between a restricting state (see FIG. 3) in which the flow of the hydraulic oil in the first locking oil passage 141 is restricted, and an allowing state (see FIG. 4) in which the flow of the hydraulic oil in the first locking oil passage 141 is allowed. In the present example embodiment, in a case where the shut-off valve 150 is in the restricting state, the flow of the hydraulic oil in the first locking oil passage 141 is restricted. Here, the state in which “the flow of the hydraulic oil is restricted” includes not only a state in which the flow of the hydraulic oil in the first locking oil passage 141 is completely restricted, but also a state in which the hydraulic oil slightly flows. The shut-off valve 150 can perform the switching by an action of a solenoid or the like, for example. In the present example embodiment, the shut-off valve 150 performs a switching operation in conjunction with the switching operation by the switching valve 110. Specifically, the shut-off valve 150 operates in conjunction with the switching valve 110 so as to be in the restricting state in a case where the switching valve 110 is in the attachment-cylinder-side feeding state, and to be in the allowing state in a case where the switching valve 110 is in the locking-cylinder-side flowing state.

[0068] The connecting oil passage 160 connects an intermediate portion of the first locking oil passage 141 and an intermediate portion of the second locking oil passage 142. As the connecting oil passage 160 is provided, the hydraulic oil is allowed to flow between the first locking oil passage 141 and the second locking oil passage 142. As illustrated in FIG. 3, the connecting oil passage 160 is connected to the upstream oil passage 141a of the first locking oil passage 141.

[0069] A throttle portion 161 to adjust the flow rate of the hydraulic oil flowing in the connecting oil passage 160 is provided in an intermediate portion of the connecting oil passage 160. As the throttle portion 161 is provided, the flow rate of the hydraulic oil flowing between the first locking oil passage 141 and the second locking oil passage 142 can be adjusted. As the throttle portion 161, a throttle valve can be used. The throttle portion 161 only needs to be able to adjust the flow rate of the hydraulic oil flowing in one direction (the direction from the second locking oil passage 142 toward the first locking oil passage 141 (the upstream oil passage 141a) in the present example embodiment) of the flowing directions of the connecting oil passage 160.

[0070] The throttle portion 161 can adjust the flow rate of the hydraulic oil in the connecting oil passage 160 so that the hydraulic oil is less likely to flow in the connecting oil passage 160 than in the first locking oil passage 141 and the second locking oil passage 142, for example. Also, the throttle portion 161 can adjust the flow rate of the hydraulic oil in the connecting oil passage 160 so that the hydraulic oil more easily flows in the connecting oil passage 160 than in the first locking oil passage 141 closed by the shut-off valve 150, for example.

[0071] The above is the description of the configuration of the hydraulic circuit 100. With the hydraulic circuit 100, operations of the attachment cylinders 14 and the locking cylinder 22 can be controlled. In the following, control on the respective cylinders using the hydraulic circuit 100 is described.

[0072] First, referring to FIGS. 3 and 4, the control to be performed when the hydraulic circuit 100 is switched between a state in which the attachment cylinders 14 are operable and a state in which the locking cylinder 22 is operable is described.

[0073] FIG. 3 illustrates the hydraulic circuit 100 in the state where the attachment cylinders 14 are operable. In this state, the switching valve 110 is in the attachment-cylinder-side feeding state, and the shut-off valve 150 is in the restricting state. In a case where the switching valve 110 is in the attachment-cylinder-side feeding state, the first port 111 and the third port 113 are opened to allow the flow of the hydraulic oil into the first attachment oil passage 131 and the second attachment oil passage 132, while the second port 112 and the fourth port 114 are closed to restrict the flow of the hydraulic oil into the first locking oil passage 141 and the second locking oil passage 142. In the state illustrated in FIG. 3, the hydraulic oil that has been fed through the feed-source-side oil passage 120 is fed to the attachment cylinders 14 in response to an operation by the worker using an operating tool in the cabin 8, and thus, the attachment cylinders 14 can be made to elongate and contract, to rock the bucket 30.

[0074] The worker can switch the hydraulic circuit 100 from the state illustrated in FIG. 3 to the state in which the locking cylinder 22 is operable as illustrated in FIG. 4, by performing an operation using an operating tool in the cabin 8. In a case where the switching operation is performed, the switching valve 110 is switched to the locking-cylinder-side flowing state, and the shut-off valve 150 is switched to the allowing state. In a case where the switching valve 110 is in the locking-cylinder-side flowing state, the second port 112 and the fourth port 114 are opened to allow the flow of the hydraulic oil into the first locking oil passage 141 and the second locking oil passage 142, while the first port 111 and the third port 113 are closed to restrict the flow of the hydraulic oil into the first attachment oil passage 131 and the second attachment oil passage 132. In the state illustrated in FIG. 4, the hydraulic oil that has been fed through the feed-source-side oil passage 120 is fed to the locking cylinder 22 in response to an operation by the worker using an operating tool in the cabin 8, and thus, the locking cylinder 22 can be made to elongate and contract, to remove the bucket 30.

[0075] Also, the worker can switch the hydraulic circuit 100 from the state illustrated in FIG. 4 to the state illustrated in FIG. 3, by performing an operation to switch the switching valve 110 to the attachment-cylinder-side feeding state and switch the shut-off valve 150 to the restricting state, using an operating tool in the cabin 8.

[0076] Next, referring to FIGS. 5A and 5B, the flow of the hydraulic oil in a case where the locking cylinder 22 is elongated and the flow of the hydraulic oil in a case where the locking cylinder 22 is contracted in the hydraulic circuit 100 in the state where the locking cylinder 22 is operable (the switching valve 110 is in the locking-cylinder-side flowing state) are described. Note that, in the example illustrated in FIGS. 5A and 5B, the direction in which the hydraulic oil flows in each oil passage is indicated by an arrow, and the portion of each oil passage in which the hydraulic pressure rises as the hydraulic oil is fed is indicated by a bold line.

[0077] Referring first to FIG. 5A, the flow of the hydraulic oil in a case where the locking cylinder 22 is elongated is described. In the case where the locking cylinder 22 is elongated, the hydraulic oil from the feed source side is fed to the switching valve 110 through both the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122. By the hydraulic oil, substantially the same hydraulic pressures are applied to the first locking oil passage 141 connected to the bottom side of the cylinder tube 22a of the locking cylinder 22, and to the second locking oil passage 142 connected to the rod side of the cylinder tube 22a.

[0078] The piston 22c of the locking cylinder 22 is subject to substantially the same hydraulic pressures from both the bottom side and the rod side of the cylinder tube 22a. Here, of the piston 22c, the area on the rod side is smaller than the area on the bottom side, because the cylinder rod 22b is provided on the rod side. Therefore, in a case where substantially the same hydraulic pressures are applied from both the bottom side and the rod side, the force acting on the piston 22c is greater on the bottom side. As the piston 22c is pushed by the bottom-side hydraulic oil, and the cylinder rod 22b moves, the locking cylinder 22 elongates.

[0079] With the above configuration, the operation of elongating the locking cylinder 22 can be performed quickly. That is, in the above configuration, in a case where a configuration in which the hydraulic oil in the first feed-source-side oil passage 121 can be merged with the hydraulic oil flowing in the second feed-source-side oil passage 122 (the hydraulic oil to be fed to the first locking oil passage 141) is adopted, when the locking cylinder 22 is elongated, the hydraulic oil discharged from the rod side of the cylinder tube 22a can be used as the hydraulic oil to be fed to the bottom side of the cylinder tube 22a. Thus, the responsiveness of the locking cylinder 22 can be enhanced.

[0080] Referring next to FIG. 5B, the flow of the hydraulic oil in a case where the locking cylinder 22 is contracted is described. In the case where the locking cylinder 22 is contracted, the hydraulic oil from the feed source side flows in the first feed-source-side oil passage 121 and is fed to the switching valve 110. The hydraulic oil flows into the second locking oil passage 142 through the fourth port 114, and is fed to the rod side of the cylinder tube 22a of the locking cylinder 22. As the piston 22c is pushed by the hydraulic oil fed to the rod side, and the cylinder rod 22b moves, the locking cylinder 22 contracts.

[0081] Further, in conjunction with the movement of the cylinder rod 22b, the hydraulic oil on the bottom side of the cylinder tube 22a is discharged from the locking cylinder 22. The discharged hydraulic oil flows into the first locking oil passage 141, and is fed to the switching valve 110 through the second port 112. The hydraulic oil flows into the second feed-source-side oil passage 122, and is returned to the feed source side.

[0082] The above is the description of flows of the hydraulic oil in cases where the locking cylinder 22 is elongated and contracted. In the hydraulic circuit 100, the throttle portion 161 is provided in the connecting oil passage 160. Accordingly, it is possible to allow the hydraulic oil to actively flow in the first locking oil passage 141 and the second locking oil passage 142, and to prevent the hydraulic oil from actively flowing in the connecting oil passage 160. Thus, it is possible to reduce the influence on operations of the locking cylinder 22 due to the connecting oil passage 160 having a flow of the hydraulic oil that is used for operations of elongating and contracting the locking cylinder 22.

[0083] Next, the flow of the hydraulic oil in the hydraulic circuit 100 in the state where the attachment cylinders 14 are operable (the switching valve 110 is in the attachment-cylinder-side feeding state) is described with reference to FIG. 3.

[0084] In a case where the attachment cylinders 14 are elongated, the hydraulic oil from the feed source side is fed to the switching valve 110 through both the first feed-source-side oil passage 121 and the second feed-source-side oil passage 122. By the hydraulic oil, substantially the same hydraulic pressures are applied to the first attachment oil passage 131 connected to the bottom sides of the cylinder tubes 14a of the attachment cylinders 14, and to the second attachment oil passage 132 connected to the rod sides of the cylinder tubes 14a. As a result, like the locking cylinder 22 described above, the attachment cylinders 14 elongate, because of the difference between the area on the rod side and the area on the bottom side of each piston 14c. With the configuration, the responsiveness of the attachment cylinders 14 is enhanced, and the bucket 30 can quickly perform a dumping action.

[0085] Further, in a case where the attachment cylinders 14 are contracted, the hydraulic oil that has flowed from the feed source side through the first feed-source-side oil passage 121 and been fed to the switching valve 110 is then fed to the rod sides of the attachment cylinders 14 through the third port 113. As the piston 14c is pushed by the fed hydraulic oil, and the cylinder rods 14b move, the attachment cylinders 14 contract. Further, in conjunction with the movement of the cylinder rods 14b, the hydraulic oil discharged from the bottom sides of the cylinder tubes 14a flows through the first attachment oil passage 131, and is fed to the switching valve 110 through the first port 111. The hydraulic oil flows into the second feed-source-side oil passage 122, and is returned to the feed source side.

[0086] In the above manner, the worker can elongate and contract the attachment cylinders 14, using the hydraulic circuit 100 according to the present example embodiment. As described above, in the hydraulic circuit 100 according to the present example embodiment, the oil passages (the first attachment oil passage 131 and the second attachment oil passage 132) on the side of the attachment cylinders 14, and the oil passages (the first locking oil passage 141 and the second locking oil passage 142) on the side of the locking cylinder 22 are connected to the respective ports of the common switching valve 110. That is, the oil passages on the side of the attachment cylinder 14 and the oil passages on the side of the locking cylinder 22 are indirectly connected through the common switching valve 110. On the other hand, the oil passages on the side of the attachment cylinders 14 and the oil passages on the side of the locking cylinder 22 are not connected by some other oil passage or the like.

[0087] In the hydraulic circuit 100 as described above, there is a possibility that the hydraulic oil will unintentionally flow from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22 due to leakage of the hydraulic oil at the switching valve 110.

[0088] In the following, a flow of hydraulic oil leaking through the switching valve 110 is described, with reference to a conventional hydraulic circuit 40 illustrated in FIG. 6. Note that the hydraulic circuit 40 has substantially the same configuration as the hydraulic circuit 100, except that the connecting oil passage 160 is not provided therein. Therefore, in the following, the hydraulic circuit 40 having components denoted by the same reference signs as those in the hydraulic circuit 100 is used in the description.

[0089] FIG. 6 illustrates an example in which the attachment cylinders 14 are contracted in the hydraulic circuit 40 in a state where the attachment cylinders 14 are operable. In this case, the hydraulic oil that has flowed from the feed source side through the first feed-source-side oil passage 121 and been fed to the switching valve 110 is then fed to the rod sides of the attachment cylinders 14 through the third port 113.

[0090] Here, the third port 113 and the fourth port 114 of the switching valve 110 are adjacent to each other. Therefore, the hydraulic oil flowing through the third port 113 leaks through the adjacent fourth port 114 to flow into the second locking oil passage 142 in some cases. In such a case, a force is applied to the locking cylinder 22 in a contracting direction by the hydraulic oil fed to the rod side through the second locking oil passage 142. In this case, in conjunction with the movement of the cylinder rod 22b, the hydraulic oil on the bottom side of the locking cylinder 22 flows into the downstream oil passage 141b of the first locking oil passage 141, and the hydraulic pressure in the downstream oil passage 141b becomes higher than the hydraulic pressure in the upstream oil passage 141a.

[0091] In this state, the hydraulic oil easily flows from the downstream oil passage 141b into the upstream oil passage 141a. Although the shut-off valve 150 is provided between the downstream oil passage 141b and the upstream oil passage 141a, even in a case where the shut-off valve 150 is provided, the hydraulic oil slightly passes through the shut-off valve 150, and the hydraulic oil on the bottom side of the locking cylinder 22 easily leaks to the side of the switching valve 110. As a result, in the hydraulic circuit 40, the locking cylinder 22 might unintentionally contract.

[0092] In the hydraulic circuit 100 according to the present example embodiment, on the other hand, even in a case where the hydraulic oil flows from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22 due to leakage through the switching valve 110, contraction of the locking cylinder 22 is prevented.

[0093] In the following, flows of the hydraulic oil in an oil passage on the side of the locking cylinder 22 in the hydraulic circuit 100 in the state where the attachment cylinders 14 are operable are described with reference to FIGS. 7A and 7B. FIGS. 7A and 7B each illustrate an example in which the hydraulic oil flows from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22 (the second locking oil passage 142) due to leakage from the third port 113 to the fourth port 114 of the switching valve 110. Note that, in the description below, flows of the hydraulic oil in the oil passages on the side of the attachment cylinder 14 are not explained.

[0094] As illustrated in FIG. 7A, in a case where the hydraulic oil flows into the second locking oil passage 142 in conjunction with the leakage of the hydraulic oil, the hydraulic pressure on the rod side of the locking cylinder 22 (the hydraulic pressure in the second locking oil passage 142) becomes higher than the hydraulic pressure on the bottom side (the hydraulic pressure in the downstream oil passage 141b of the first locking oil passage 141). Here, in the hydraulic circuit 100, the second locking oil passage 142 and the upstream oil passage 141a of the first locking oil passage 141 are connected by the connecting oil passage 160. Therefore, in the hydraulic circuit 100, the hydraulic oil from the second locking oil passage 142 flows into the upstream oil passage 141a through the connecting oil passage 160, and the hydraulic pressures in the second locking oil passage 142 and the upstream oil passage 141a become substantially equal. In this case, the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 is higher than the hydraulic pressure in the downstream oil passage 141b.

[0095] As described above, in a case where the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 is made higher than the hydraulic pressure in the downstream oil passage 141b, it is possible to prevent the hydraulic oil on the bottom side of the locking cylinder 22 from leaking to the side of the switching valve 110 through the first locking oil passage 141. Thus, contraction of the locking cylinder 22 is prevented, and unintended detachment of the bucket 30 from the attachment mounting mechanism 20 is prevented.

[0096] FIG. 7B illustrates a state in which the hydraulic pressure on the bottom side of the locking cylinder 22 (the hydraulic pressure in the downstream oil passage 141b of the first locking oil passage 141) is higher than the hydraulic pressure on the rod side (the hydraulic pressure in the second locking oil passage 142). In this case, the hydraulic oil in the downstream oil passage 141b of the first locking oil passage 141 having a relatively high hydraulic pressure slightly flows into the upstream oil passage 141a through the shut-off valve 150. As a result, the locking cylinder 22 slightly contracts.

[0097] As the hydraulic oil flows, the hydraulic pressure in the downstream oil passage 141b of the first locking oil passage 141 gradually drops. Along with this, the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 and the hydraulic pressure in the second locking oil passage 142 connected to the upstream oil passage 141a through the connecting oil passage 160 both rise.

[0098] At the time when the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 becomes equal to or higher than the hydraulic pressure in the downstream oil passage 141b, the flow of the hydraulic oil from the downstream oil passage 141b into the upstream oil passage 141a stops. Accordingly, the locking cylinder 22 does not contract any more. In a case where the hydraulic pressure in the upstream oil passage 141a of the first locking oil passage 141 becomes higher than the hydraulic pressure in the downstream oil passage 141b, the hydraulic circuit 100 is in a state that is substantially the same as the state illustrated in FIG. 7A. With the configuration, contraction of the locking cylinder 22 is prevented, and unintended detachment of the bucket 30 from the attachment mounting mechanism 20 is prevented.

[0099] As described above, in the hydraulic circuit 100 according to the present example embodiment, it is possible to prevent unintended contraction of the locking cylinder 22, regardless of the state of the hydraulic pressure in the locking cylinder 22 (a state in which the hydraulic pressure on bottom side is high, or a state in which the hydraulic pressure on the rod side is high).

[0100] Also, in the hydraulic circuit 100 according to the present example embodiment, the connecting oil passage 160 is connected not to the downstream oil passage 141b of the first locking oil passage 141, but to the upstream oil passage 141a, and thus, unintended elongation of the locking cylinder 22 is prevented. That is, in a case where the connecting oil passage 160 is connected to the downstream oil passage 141b, there is a possibility that the hydraulic oil in the downstream oil passage 141b will be fed directly to the bottom side of the locking cylinder 22, as the hydraulic oil flows from an oil passage on the side of the attachment cylinder 14 into an oil passage on the side of the locking cylinder 22 due to leakage at the switching valve 110. Because of this, there is a possibility that the locking cylinder 22 will unintentionally elongate.

[0101] On the other hand, in a case where the connecting oil passage 160 is connected to the upstream oil passage 141a of the first locking oil passage 141 as in the hydraulic circuit 100 according to the present example embodiment, the shut-off valve 150 limits the flow rate of the hydraulic oil from the upstream oil passage 141a into the downstream oil passage 141b. Thus, unintended elongation of the locking cylinder 22 is prevented.

[0102] As described above, the hydraulic circuit 100 according to the present example embodiment includes the locking cylinder 22 to elongate and contract to switch between a fixed state in which the bucket 30 (an attachment) is fixed to the front loader 10 (a loader) and a released state in which fixing of the bucket 30 to the front loader 10 is canceled, the first locking oil passage 141 through which the hydraulic oil to be fed to the locking cylinder 22 flows to put the locking cylinder 22 into the fixed state, the second locking oil passage 142 through which the hydraulic oil to be fed to the locking cylinder 22 flows to put the locking cylinder 22 into the released state, and the connecting oil passage 160 that connects the first locking oil passage 141 and the second locking oil passage 142 and includes a throttle portion 161 to adjust the flow rate of the hydraulic oil flowing between the first locking oil passage 141 and the second locking oil passage 142.

[0103] With such a configuration, unintended detachment of the bucket 30 is prevented. Specifically, in a conventional hydraulic circuit, in a case where hydraulic oil leaking from some other portion (an attachment cylinder 14 or the like, for example) is fed to the second locking oil passage 142, the hydraulic pressure in the second locking oil passage 142 might become higher than the hydraulic pressure in the first locking oil passage 141. In this case, the hydraulic oil in the locking cylinder 22 leaks through the first locking oil passage 141. As a result, the locking cylinder 22 might unintentionally contract, and the attachment might be easily detached. On the other hand, the first locking oil passage 141 and the second locking oil passage 142 are connected through the connecting oil passage 160 as in the hydraulic circuit 100 according to the present example embodiment, so that the first locking oil passage 141 and the second locking oil passage 142 are kept at equal or substantially equal pressures. Thus, leakage of the hydraulic oil in the locking cylinder 22 through the first locking oil passage 141 is prevented, and contraction of the locking cylinder 22 is prevented. Also, as the throttle portion 161 is provided in the connecting oil passage160, an active flow of the hydraulic oil in the connecting oil passage 160 is prevented when the locking cylinder 22 is intentionally operated. Thus, the influence on the operation of the locking cylinder 22 is reduced.

[0104] Further, the hydraulic circuit 100 includes the shut-off valve 150 to restrict the flow of the hydraulic oil in the first locking oil passage 141, and the connecting oil passage 160 is connected to the side of the feed source of the hydraulic oil with respect to the shut-off valve 150 in the first locking oil passage 141.

[0105] With such a configuration, unintended elongation of the locking cylinder 22 is prevented. Specifically, as the connecting oil passage 160 is connected to the first locking oil passage 141 at a portion closer to the feed source than the shut-off valve 150, the amount of feed of the hydraulic oil to the locking cylinder 22 can be limited in a case where the hydraulic oil leaking from some other portion (an attachment cylinder 14 or the like, for example) in the hydraulic circuit 100 is supplied to the first locking oil passage 141 through the connecting oil passage 160. Thus, unintended elongation of the locking cylinder 22 is prevented.

[0106] Further, the hydraulic circuit 100 includes the switching valve 110 to switch between a state in which the hydraulic oil from the feed source is fed to the side of the locking cylinder 22, and a state in which the hydraulic oil is fed to the side of another cylinder different from the locking cylinder 22, and another oil passage through which the hydraulic oil to be fed from the switching valve 110 to the another cylinder flows, and the first locking oil passage 141, the second locking oil passage 142, and the another oil passage are each connected to the switching valve110.

[0107] With such a configuration, it is possible to prevent unintended contraction of the locking cylinder 22 due to the hydraulic oil leaking from another oil passage through the switching valve 110.

[0108] Further, a front loader 10 (a loader) according to an example embodiment includes the hydraulic circuit 100 according to the present example embodiment.

[0109] With such a configuration, unintended detachment of the bucket 30 is prevented.

[0110] Furthermore, a tractor 1 (a working machine) according to an example embodiment includes the front loader 10 according to the present example embodiment.

[0111] With such a configuration, unintended detachment of the bucket 30 is prevented.

[0112] Note that the tractor 1 according to the present example embodiment is an example embodiment of a working machine according to the present disclosure.

[0113] Also, the front loader 10 according to the present example embodiment is an example embodiment of a loader according to the present disclosure.

[0114] Further, the bucket 30 according to the present example embodiment is an example embodiment of an attachment according to the present disclosure.

[0115] Although some example embodiments of the present disclosure have been described so far, the present disclosure is not limited to the above configurations, and various modifications can be made to it within the scope of the present invention.

[0116] For example, the shape of each of the structural elements (the front loader 10, the bucket 30, and the like), the configuration of the hydraulic circuit 100, and the like described in the above example embodiments are merely examples, and are not limited to the example embodiments described above.

[0117] Specifically, in the hydraulic circuits 100 according to the present example embodiments, when the respective cylinders (the attachment cylinders 14 and the locking cylinder 22) are elongated, the hydraulic oil is fed to both the bottom side and the rod side of each cylinder, and each cylinder is elongated by taking advantage of the difference in area of each piston. However, the present disclosure is not limited to this. For example, it is also possible to adopt a configuration in which the hydraulic oil is fed only to the rod side, and the hydraulic oil on the bottom side is discharged from each cylinder when each cylinder is elongated.

[0118] Also, in the examples described in the above example embodiments, the connecting oil passage 160 is connected to the upstream oil passage 141a of the first locking oil passage 141. However, the present disclosure is not limited to this. For example, the connecting oil passage 160 can be connected to the downstream oil passage 141b. In this case, even if the hydraulic oil leaks from an oil passage on the side of the attachment cylinders 14 into an oil passage on the side of the locking cylinder 22, the areas of the piston 22c of the locking cylinder 22 on the bottom side and the rod side can be set as appropriate to prevent unintended elongation of the locking cylinder 22.

[0119] Further, in the above example embodiments, the bucket 30 has been described as an example of the attachment. However, the attachment is not limited to this configuration. As the attachment, various kinds of attachments (a roll grab, a fork, and the like, for example) that can be attached to the front loader 10 can be adopted, instead of or in addition to the bucket 30, for example.

[0120] Also, in the examples described in the above example embodiment, the tractor 1 has been described as an example of the working machine. However, the working machine is not limited to such a machine. For example, a working machine may be some other agricultural vehicle, a construction vehicle, an industrial vehicle, or the like.

[0121] While example embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Examples

Embodiment Construction

[0025]In the following description, directions indicated by an arrow U, an arrow D, an arrow F, an arrow B, an arrow L, and an arrow R in the drawings are defined as an upward direction, a downward direction, a frontward direction, a backward direction, a leftward direction, and a rightward direction, respectively.

[0026]First, the overall configuration of a tractor 1 according to an example embodiment of the present disclosure is described.

[0027]The tractor 1 mainly includes a machine body frame 2, an engine 3, a transmission casing 4, front wheels 5, rear wheels 6, a hood 7, a cabin 8, a steering wheel 9, and a front loader 10.

[0028]The machine body frame 2 is a structure including a combination of panels. The machine body frame 2 preferably has a substantially rectangular shape in a planar view. The machine body frame 2 is positioned with a longitudinal direction of the machine body frame 2 oriented in the front-back direction. The engine 3 is fixed to a rear portion of the machin...

Claims

1. A hydraulic circuit comprising:a locking cylinder to elongate and contract to switch between a fixed state in which an attachment is fixed to a loader and a released state in which fixing of the attachment to the loader is canceled;a first locking oil passage through which hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the fixed state;a second locking oil passage through which the hydraulic oil to be fed to the locking cylinder flows to put the locking cylinder into the released state; anda connecting oil passage that connects the first locking oil passage and the second locking oil passage, and includes a throttle portion to adjust a flow rate of the hydraulic oil flowing between the first locking oil passage and the second locking oil passage.

2. The hydraulic circuit according to claim 1, further comprising:a shut-off valve to restrict flowing of the hydraulic oil in the first locking oil passage; whereinthe connecting oil passage is connected to a side of a feed source of the hydraulic oil with respect to the shut-off valve in the first locking oil passage.

3. The hydraulic circuit according to claim 1, further comprising:a switching valve to switch between a state in which the hydraulic oil from a feed source is fed to a side of the locking cylinder, and a state in which the hydraulic oil is fed to a side of another cylinder different from the locking cylinder; andanother oil passage through which the hydraulic oil to be fed from the switching valve to the another cylinder flows; whereineach of the first locking oil passage, the second locking oil passage, and the another oil passage are connected to the switching valve.

4. A loader comprising the hydraulic circuit according to claim 1.

5. A working machine comprising the loader according to claim 4.

6. A loader comprising the hydraulic circuit according to claim 2.

7. A working machine comprising the loader according to claim 6.

8. A loader comprising the hydraulic circuit according to claim 3.

9. A working machine comprising the loader according to claim 8.

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