loader

Abstract

In a loader equipped with a leveling mechanism using a flow diversion valve, the scuffing phenomenon during fine adjustment of the lift arm's descent is eliminated, and stable parallel descent is achieved even during fine adjustment of the lift arm's descent. [Solution] The loader of the present invention comprises a work implement (bucket 32) at the tip of a lift arm, a lift cylinder 27, a dump cylinder 41, and a first switching valve 51 and a second switching valve 52 connected in parallel to a hydraulic supply source (hydraulic pump P). When the lift arm is lowered more slowly and finely, the hydraulic supply source is disconnected from the lift cylinder, the rising port of the lift cylinder is connected to the squeegee port of the dump cylinder and the hydraulic tank via the flow divider, and the dump port of the dump cylinder is connected to the lowering port of the lift cylinder via a check valve.

Description

Technical Field

[0001] The present invention relates to a loader that is mounted on a work vehicle such as a tractor and raises and lowers heavy objects with a working implement such as a bucket.

Background Art

[0002] A working implement is an attachment device that is detachably mounted on a work vehicle such as a tractor. As shown in FIG. 3, a working implement mounted on the front side of the tractor 10 is called a front loader 21. This front loader 21 has lift arms 23 that are raised and lowered by lift cylinders 27, and various tip attachments such as a bucket 32, forks, graders, roll grabs, container buckets, loading hooks, etc. are attached to the tips of the lift arms 23 according to the work content.

[0003] Hereinafter, it will be described assuming that the attachment is the bucket 32. As shown in FIG. 3, a dump cylinder 41 is disposed at the upper part of the tip side of the lift arm 23, and the bucket 32 is configured to tilt forward (dump operation) or tilt backward (squee operation) by this dump cylinder 41.

[0004] The raising and lowering operation of the lift arm 23 and the dump and squee operations of the bucket 32 are performed by operating, for example, a joystick-type operation lever provided in the driver's seat of the tractor 10 in the front-back, left-right directions. The operation lever can perform composite operations such as raising or lowering the lift arm 23 while dumping or squee-ing the bucket 32, in addition to the individual operations of raising and lowering the lift arm 23 and dumping and squee-ing the bucket 32.

[0005] Incidentally, the hydraulic circuit of the front loader 21 is known to be equipped with a leveling mechanism to prevent the load from falling or collapsing. Examples of front loaders equipped with this leveling mechanism include the front loaders described in Patent Document 1 (Japanese Patent Publication No. 6-88351) and Patent Document 2 (Japanese Patent Publication No. 3542373), and the front loader described in Non-Patent Document 1 (hereinafter referred to as the MX front loader). With this leveling mechanism, the bucket 32 ​​dumps or scoops simultaneously with the lifting and lowering operation of the lift arm 23, and the angle of the bucket 32 ​​with respect to the ground is maintained at a nearly constant level.

[0006] The front loader and MX front loader described in Patent Document 1 have an auxiliary cylinder installed adjacent to the upper side of the lift cylinder 27, and this auxiliary cylinder maintains the parallelism (horizontalness to the ground) of the bucket 32 ​​(parallel raising and lowering of the bucket). Leveling mechanisms using auxiliary cylinders have the drawbacks of increased costs due to the auxiliary cylinder and its piping, and the difficulty in selecting the type of cylinder (same diameter double rod type, different diameter double rod type, single rod type, etc.) to match the volume ratio of the dump cylinder 41 and the auxiliary cylinder.

[0007] On the other hand, the front loader described in Patent Document 2 connects the lowering port of the lift cylinder 27 to the dump port of the dump cylinder 41 during parallel upward movement, and connects the upward port of the lift cylinder 27 to the squeezing port of the dump cylinder 41 during parallel downward movement, by operating the first and second switching valves. This type of leveling mechanism does not use an auxiliary cylinder, so it does not have the aforementioned problems. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-88351 [Patent Document 2] Patent No. 3542373 [Non-patent literature]

[0009] [Non-Patent Document 1] "MX, Agricultural equipment manufacturer" (searched September 25, 2024), T400 series front loader from MX, a French company, Internet<URL:https: / / m-x.eu / en / > [Overview of the project] [Problems that the invention aims to solve]

[0010] However, it was found that the leveling mechanism described in Patent Document 2 has the following problems. Specifically, both the lift cylinder 27 and the dump cylinder 41 use a single-rod double-acting type, and when the lift cylinder 27 is raised, the entire amount of pressurized oil that comes out of the lowering port (rod side) is supplied to the dump port (head side) of the dump cylinder 41. Also, when the lift cylinder 27 is lowered, a portion of the pressurized oil that comes out of the rising port (head side) is supplied to the squeezing port (rod side) of the dump cylinder 41, and the remaining pressurized oil is returned to the hydraulic tank via the flow divider 52 shown in Figures 4A and 4B.

[0011] The reason the remaining pressurized oil is returned to the hydraulic tank via the flow divider valve 52 is that the lift and dump are configured to rise in parallel by matching the volume of the lowering and dumping of the single-rod cylinders. If the lifting port and the squeezing port of the single-rod cylinder of the lift and dump are connected during the lowering phase, the volume ratio of the cylinders will not match, resulting in excessive squeezing and preventing parallel lowering. In Figures 4A and 4B, Ps is the squeezing side pressure and Pt is the tank side pressure.

[0012] The throttle diameters S and T are selected so that there are no problems when the lift cylinder 27 is lowered by the pump flow rate. However, if the operator moves the joystick-type control lever slightly and lowers the lift cylinder 27 at a speed slower than the lowering speed due to the pump flow rate (reducing the amount of oil supplied to the flow divider valve), it becomes impossible to set the flow divider valve 52 to the normal flow divider state.

[0013] In other words, the head-side volume L of the lift cylinder 27 is almost entirely due to the weight of the lift arm. H When the pressurized oil discharged from the loader is divided into the scoop side and the tank side by the flow divider valve 52, and fine adjustments are made to the descent, the flow rate of pressure Pu entering the flow divider valve 52 decreases, making it impossible to maintain the normal flow division state. In the case of loaders, they are designed to scoop slightly for safety reasons, but if the amount of oil supplied to the flow divider valve decreases hydraulically, the flow division ratio changes, making parallel descent impossible.

[0014] Here, "normal flow division state" refers to a constant ratio flow division state determined by the area ratio of the scoop-side throttle S and the tank-side throttle T of the flow division valve 52. Since the pressure difference between the scoop-side throttle S and the tank-side throttle T is proportional to the square of the flow rate, the phenomenon of the bucket 32 ​​becoming scoopy becomes more pronounced as the fine adjustment descent speed slows down.

[0015] As an operator, I would like the loader function to provide stable, parallel descent that is not affected by the descent speed of the lift arm 23. However, the scuffing phenomenon during fine-tuning descent is due to the structure of the diversion valve itself, and so far, no suitable solution has been found. It is conceivable to add and install multiple diversion valves in addition to the current diversion valve, each with progressively smaller scuffing-side throttle S and tank-side throttle T, and select the optimal diversion valve that provides a proper diversion state according to the flow rate entering the diversion valve. However, considering the cost and installation space of multiple diversion valves, this is not a realistic solution.

[0016] Therefore, the problem that the present invention aims to solve is to eliminate the scuffing phenomenon during fine adjustment of the lift arm when lowering a loader having a leveling mechanism using a flow divider valve, and to achieve stable parallel lowering even when fine adjustment of the lift arm is being made. [Means for solving the problem]

[0017] To solve the aforementioned problems, the loader according to the present invention comprises a lift arm supported on a support bracket of a work vehicle so as to be able to move up and down, a work machine supported on the tip of the lift arm so as to be able to swing up and down, a single-rod double-acting lift cylinder disposed between the support bracket and the lift arm and raising and lowering the lift arm by extension and retraction, a single-rod double-acting dump cylinder disposed between the lift arm and the work machine and swinging the work machine up and down by extension and retraction, and a first switching valve and a second switching valve connected in parallel to a hydraulic supply source. The first switching valve is switchable to the N (neutral) position, the raised position and the lowered position in order to operate the lift cylinder, and the second switching valve is switchable to the N (neutral) position, the dump position and the squeezing position in order to operate the dump cylinder, and a brake valve is disposed between the squeezing port of the dump cylinder and the hydraulic tank to prevent the dump cylinder from moving on its own when the first switching valve is operated to the raised position, and when the first switching valve is operated to the lowered position the raised port of the lift cylinder In a loader having a flow divider valve that divides pressurized oil from the port to the squee port of the dump cylinder and the hydraulic tank, when the lift arm is raised by setting the first switching valve to the raised position and the second switching valve to the N position, the hydraulic supply source is connected to the raised port of the lift cylinder, the lowering port of the lift cylinder is connected to the dump port of the dump cylinder, the brake valve is activated by the pressure of the dump port to connect the squee port to the hydraulic tank, and the first switching valve is set to the lowering position and the front When the lift arm is lowered with the second switching valve in the N position, the hydraulic supply source is connected to the lowering port of the lift cylinder, the rising port of the lift cylinder is connected to the squeezing port of the dump cylinder and the hydraulic tank via a flow divider, and the dump port of the dump cylinder is connected to the hydraulic tank, and when the lift arm is lowered even more slowly and finely with the first switching valve in the fine adjustment lowering position and the second switching valve in the N position, the hydraulic supply source is disconnected from the lift cylinder,Connect the ascending port of the lift cylinder to the squirt port of the dump cylinder and the hydraulic tank via the flow dividing valve, and connect the dump port of the dump cylinder to the descending port of the lift cylinder via a check valve.

[0018] According to the loader of the present invention, it is possible to eliminate the squirt increase phenomenon during the fine adjustment descent of the lift arm and achieve stable parallel descent even during the fine adjustment descent of the lift arm.

Brief Description of the Drawings

[0019] [Figure 1] It is a hydraulic circuit diagram of a loader according to an embodiment of the present invention. [Figure 2A] It is a diagram for explaining the parallel ascending circuit of the loader. [Figure 2B] It is a diagram for explaining the parallel descending circuit of the loader. [Figure 2C] It is a diagram for explaining the parallel descending circuit during the fine adjustment descent of the loader. [Figure 3] It is a side view of a general front loader mounted on the front side of a tractor. [Figure 4A] It is a cross-sectional view for explaining the neutral state of the flow dividing valve used in the leveling mechanism of Patent Document 2. [Figure 4B] It is a cross-sectional view for explaining the operating state of the flow dividing valve used in the leveling mechanism of Patent Document 2. [Figure 5] It is a hydraulic circuit diagram of the loader of Patent Document 2. [Figure 5A] It is a diagram for explaining the parallel ascending circuit of the loader. [Figure 5B] It is a diagram for explaining the parallel descending circuit of the loader. [Figure 5C] It is a diagram for explaining the parallel descending circuit during the fine adjustment descent of the loader.

Modes for Carrying Out the Invention

[0020] Hereinafter, a loader according to an embodiment of the present invention will be described with reference to the drawings. As shown in Figure 3, a bucket 32 ​​as an attachment is mounted on the tip of a lift arm 23 that constitutes the main body of the front loader 21 so as to be able to swing up and down. The base end of the lift arm 23 is attached to a support bracket 22 which serves as a support base and is fixedly provided on the tractor 10 in Figure 3.

[0021] A lift cylinder 27 is positioned between the support bracket 22 and the longitudinal middle portion of the lift arm 23. The lift arm 23 is raised and lowered by the extension and retraction of the lift cylinder 27. The lift cylinder 27 is a single-rod double-acting hydraulic cylinder, with its base end (head side) connected to the support bracket 22 and its rod side connected to the lift arm 23.

[0022] A dump cylinder 41 is positioned above the longitudinal middle section of the lift arm 23. The dump cylinder 41 is a single-rod double-acting hydraulic cylinder, similar to the lift cylinder 27, with its head supported by the lift arm 23 and its rod connected to the bucket 32 ​​via a link.

[0023] The hydraulic pump P, which serves as the hydraulic power source as shown in Figure 1, is mounted on the tractor 10, and the hydraulic pump P and the front loader 21 are detachably connected via a hydraulic coupler or the like (not shown). A first switching valve 51 for the lift cylinder 27 and a second switching valve 50 for the dump cylinder 41 are connected to the hydraulic pump P. The first switching valve 51 and the second switching valve 50 can be operated individually or simultaneously by a joystick-type operating lever.

[0024] Furthermore, Figures 2A, 2B, and 2C illustrate the parallel upward circuit, parallel downward circuit, and parallel downward circuit during fine-adjustment downward when the first switching valve 51 is set to the upward position, downward position, and fine-adjustment downward position with the second switching valve 50 in the N position. In Figure 1, the N position of the first switching valve 51 and the second switching valve 50 is indicated with light gray ink. Similarly, Figures 5A, 5B, and 5C illustrate the parallel upward circuit, parallel downward circuit, and parallel downward circuit during fine-adjustment downward when the first switching valve 51 is set to the upward position, downward position, and fine-adjustment downward position with the second switching valve 50 in Figure 5 (Patent Document 2) in the N position.

[0025] As shown in Figure 1, the lowering port 27b of the lift cylinder 27 is connected to the dump port 41a of the dump cylinder 41 via a check valve 59. The squeezing port 41b of the dump cylinder 41 is connected to the hydraulic tank via a brake valve 55. The first switching valve 51 is connected to a flow divider valve 52 and check valves 60 and 61, and the second switching valve 50 is connected to a check valve 62.

[0026] The brake valve 55 is configured to use the pressure at the dump port 41a of the dump cylinder 41 as pilot pressure. As a result, when the pressure at the dump port 41a of the dump cylinder 41 rises, the pilot pressure opens the brake valve 55, connecting the squee port 41b of the dump cylinder 41 to the hydraulic tank.

[0027] Furthermore, because the load acting on the bucket 32 ​​is large when it is raised horizontally, the bucket 32 ​​may dump faster than the speed of the oil supplied to the dump port 41a of the dump cylinder 41. In such cases, the negative pressure generated in the dump port 41a immediately closes the brake valve 55, preventing the return oil from flowing from the squeezing port 41b of the dump cylinder 41. This prevents the bucket 32 ​​from dumping any further, thus preventing the load from collapsing or other damage.

[0028] ● Parallel rising circuit During parallel ascent, as shown in Figure 2A, pressurized oil from the hydraulic pump P is introduced into the ascent port 27a of the lift cylinder 27. On the other hand, the pressurized oil pushed out from the descent port 27b of the lift cylinder 27 is entirely introduced into the dump port 41a of the dump cylinder 41. In other words, parallel ascent is achieved by designing and connecting the volumes of the descent side of the lift cylinder and the dump side of the dump cylinder to match.

[0029] When pressurized oil is supplied from the lowering port 27b of the lift cylinder 27 to the dump port 41a of the dump cylinder 41, the supply pressure activates the brake valve, connecting the squeegee port 41b of the dump cylinder 41 to the tank and causing the dump cylinder 41 to dump. In other words, the brake valve activates and the dump cylinder 41 operates only when pressurized oil is supplied to the dump port 41a of the dump cylinder 41 and pressure is generated, so the bucket 32 ​​rises parallel to the ground even when the load acting on it is large.

[0030] ●Parallel descending circuit During parallel descent, as shown in Figure 2B, pressurized oil from the hydraulic pump P is introduced into the descent port 27b of the lift cylinder 27. Meanwhile, the pressurized oil pushed out from the rise port 27a of the lift cylinder 27 is divided by the flow divider 52, with a portion of the pressurized oil being supplied to the squeezing port 41b of the dump cylinder 41, and the remaining pressurized oil being returned to the hydraulic tank. On the other hand, the pressurized oil pushed out from the dump port 41a of the dump cylinder 41 is returned to the tank.

[0031] ●Parallel descending circuit (during fine adjustment descending) During fine adjustment descent, the hydraulic pump P and the lift cylinder 27 are shut off, as shown in Figure 2C. Therefore, the pressurized oil from the hydraulic pump P is not supplied to either the lift cylinder 27 or the dump cylinder 41. The lift arm 23 lowers with fine adjustment by the weight of the entire arm section, including the bucket 32.

[0032] In other words, when the first switching valve 51 is set to the fine adjustment lowered position and the second switching valve 50 is set to the N position, as shown in Figure 2C, the dump port 41a of the dump cylinder 41 is connected to the lowered port 27b of the lift cylinder 27 via the check valve 59.

[0033] On the other hand, the lifting port 27a of the lift cylinder 27 is connected to the squeezing port 41b of the dump cylinder 41 and the hydraulic tank via the flow divider 52. As a result, some of the pressurized oil from the lifting port 27a of the lift cylinder 27 is supplied to the squeezing port 41b of the dump cylinder 41, causing the dump cylinder 41 to squeeze. The remaining pressurized oil is returned to the hydraulic tank.

[0034] Conventionally, as shown in Figure 5C (Patent Document 2), even during fine adjustment of descent, pressurized oil from the hydraulic pump P was supplied to the descent port 27b of the lift cylinder 27 and returned to the hydraulic tank at the dump port 41a of the dump cylinder 41. As a result, the flow divider valve 52 could not properly divide the flow, and more pressurized oil flowed to the squeezing port, causing the bucket 32 ​​to squeeze more than horizontally and preventing parallel descent. In contrast, in this embodiment, the hydraulic pump P and the lift cylinder 27 are shut off, and pressurized oil from the dump port 41a of the dump cylinder 41 is introduced to the descent port 27b of the lift cylinder 27 via the check valve 59.

[0035] In the parallel lifting circuit described above, the volume of the lift cylinder 27's descent and the dump cylinder 41's dump are matched and connected to achieve parallel lifting. Therefore, in the parallel lowering circuit as well, parallel lowering is possible by connecting the lift cylinder 27's descent port 27b and the dump cylinder 41's dump port 41a. When the flow divider valve 52 can no longer properly divide the flow and the dump cylinder 41 attempts to increase the scuff, the pressure between the lift cylinder 27's descent port and the dump cylinder 41's dump port increases, the brake valve 55 activates, and the scuff port 41b is connected to the hydraulic tank. In other words, the excess oil volume that would result from the scuff caused by the flow divider valve 52 is returned to the hydraulic tank via the brake valve 55, and only the amount of oil necessary for parallel lowering is supplied to the dump cylinder 41's scuff port 41b, thus preventing the scuff phenomenon during fine-tuning lowering.

[0036] ●Summary Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, in the above embodiments, the orientation of the lift cylinder 27 and the dump cylinder 41 may be reversed, with the rod side and the head side being reversed. Also, the lift arm 23 is not limited to a single-piece design but can be changed to a type that can be bent in the middle of its longitudinal direction.

[0037] Furthermore, in the above embodiment, the lift arm 23 was raised and lowered by the extension and contraction of the lift cylinder 27, and the bucket 32 ​​was tilted up and down by the extension and contraction of the dump cylinder 41. However, conversely, it is also possible to configure the system so that the lift arm 23 is raised and lowered by the contraction and extension of the lift cylinder 27, and the bucket 32 ​​is tilted up and down by the contraction and extension of the dump cylinder 41.

[0038] Furthermore, the end attachment is not limited to the bucket 32; various other end attachments such as forks, graders, roll grabs, container buckets, and loading hooks can be attached. The present invention is also applicable to various work machines other than front loaders. [Explanation of symbols]

[0039] 10: Tractor 21: Front loader 22: Support bracket 23: Lift arm 27: Lift cylinder 27a: Lifting port 27b: Lowering port 32: Bucket (working equipment) 41: Dump cylinder 41a: Dump port 41b: Squeeze port 50: Second switching valve 51: First switching valve 52: Flow divider valve 55: Brake valve 59-62: Check valve P: Hydraulic pump (hydraulic power source) S: Squeegee side throttle T: Tank side restriction

Claims

[Claim 1] A lift arm supported on a support bracket of a work vehicle so as to be able to move up and down, a work machine supported on the tip of the lift arm so as to be able to swing up and down, a single-rod double-acting lift cylinder disposed between the support bracket and the lift arm and moving up and down by extension and retraction, a single-rod double-acting dump cylinder disposed between the lift arm and the work machine and swinging up and down by extension and retraction, and a first switching valve and a second switching valve connected in parallel to a hydraulic supply source, wherein the first switching valve is in the N (neutral) position in order to actuate the lift cylinder, A loader comprising: a first and second switching valve that can be switched between an upward and downward position, the second switching valve being switchable between an N (neutral) position, a dump position, and a scoop position in order to operate the dump cylinder; a brake valve disposed between the scoop port of the dump cylinder and the hydraulic tank to prevent the dump cylinder from moving on its own when the first switching valve is operated to the upward position; and a diversion valve that, when the first switching valve is operated to the downward position, diverts the pressurized oil from the upward port of the lift cylinder to the scoop port of the dump cylinder and the hydraulic tank, When the lift arm is raised by setting the first switching valve to the raised position and the second switching valve to the N position, the hydraulic supply source is connected to the rising port of the lift cylinder, the lowering port of the lift cylinder is connected to the dump port of the dump cylinder, and the brake valve is activated by the pressure of the dump port and connected to the squeezing port of the hydraulic tank, When the lift arm is lowered by setting the first switching valve to the lowered position and the second switching valve to the N position, the hydraulic supply source is connected to the lowering port of the lift cylinder, the rising port of the lift cylinder is connected to the squeezing port of the dump cylinder and the hydraulic tank via a flow divider, and the dump port of the dump cylinder is connected to the hydraulic tank, A loader characterized in that, when the first switching valve is set to the fine adjustment lowering position and the second switching valve is set to the N position to further slow down the lift arm with fine adjustment, the hydraulic supply source is disconnected from the lift cylinder, the rising port of the lift cylinder is connected to the squeezing port of the dump cylinder and the hydraulic tank via the flow divider valve, and the dump port of the dump cylinder is connected to the lowering port of the lift cylinder via a check valve.

Images