Hydraulic lifting device

Abstract

To provide a hydraulic elevating / lowering device that can increase a degree of freedom of layout of components.SOLUTION: A hydraulic elevating / lowering device 100 comprises a lift arm 2, a position control lever 6, and a position control transmission mechanism 20. The position control transmission mechanism 20 comprises a position control cam 210, a first position control shaft 220, and a second position control shaft 230. The first shaft 220 rotates around an axis A1 (and an axis A2) in accordance with displacement of the lever 6. The second shaft 230 rotates around an axis A3 in accordance with displacement of a feedback rod 9 when the lift arm 2 relatively rotates. The cam 210 displaces a spool position in accordance with rotation of each of the first and second shafts 220 and 230. The axis A3 of the second shaft 230 is located above the axis A1 of the first shaft 220.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a hydraulic lifting device that raises and lowers a lift arm based on hydraulic pressure. [Background technology]

[0002] A conventional hydraulic lifting device that uses hydraulic pressure to raise and lower a lift arm is disclosed in, for example, Patent Document 1. This device includes a hydraulic cylinder and a control valve with a spool, and allows or restricts the supply and discharge of hydraulic oil to the hydraulic cylinder depending on the position of the spool. This device also includes a position lever and an operating link mechanism. The operating link mechanism transmits the respective displacements to a lift feedback link based on the operation of the position lever and the raising and lowering of the lift arm, and the lift feedback link swings to displace the spool.

[0003] The operating link mechanism is broadly divided into a section that transmits the displacement of the position lever and a section that transmits the displacement of the lift arm. The "section that transmits the displacement of the position lever" includes a first arm shaft (arm shaft 44). One end of the first arm shaft is connected to the base of the position lever, and the other end is connected to one end of the lift feedback link. In response to rotation of the position lever, the first arm shaft rotates around its axis, causing the lift feedback link to swing. The "section that transmits the displacement of the lift arm" includes a second arm shaft (arm shaft 51). One end of the second arm shaft is connected to a rod that moves with the lift arm, and the other end is connected to the other end of the lift feedback link. In response to the elevation of the lift arm, the second arm shaft rotates around its axis, causing the lift feedback link to swing. In other words, the displacement of the lift arm is fed back to the spool via the rod. This allows the height of the lift arm in the elevation direction to be easily adjusted to the desired height. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-000003 A (paragraphs 0015 to 0021, etc.) Summary of the Invention

[0005] This type of hydraulic lifting device has many components, each of which has a wide variety of shapes and sizes. From the perspective of improving mountability on a work machine and ease of operation by an operator, there is a growing demand for greater flexibility in the layout of each component. Meanwhile, in the device of Patent Document 1, the first and second arm shafts are pivotally supported by bosses on both the left and right sides. Because the bosses are coaxially located, the first and second arm shafts are coaxially arranged to extend in the left-right direction. When the first and second arm shafts are coaxially arranged in this manner, the components must be positioned so as not to interfere with each other, which limits the layout.

[0006] In view of the above, an object of the present invention is to provide a hydraulic lifting device that allows the height of the lift arm in the lifting direction to be easily adjusted to a target height and that allows for greater freedom in the layout of component parts. [Means for solving the problem]

[0007] The technical means of the present invention for solving this technical problem is characterized by the following: The hydraulic lifting device of the present invention comprises a case, a hydraulic cylinder located inside the case and driven in response to the supply and discharge of hydraulic oil, a control valve located inside the case and having a spool in a flow path of the hydraulic oil, the control valve allowing and restricting the supply and discharge of the hydraulic oil to the hydraulic cylinder in response to the position of the spool, a lift arm located outside the case and having defined one end and the other end, the one end of which is connectable to an object and which rotates relative to the case with the other end as a fulcrum when the hydraulic cylinder is driven, thereby lifting and lowering the connected object, and a lift arm located outside the case and having defined one end and the other end of which is connectable to an object when the hydraulic cylinder is driven, the lift arm being configured to lift and lower ... a position control lever configured to be displaceable in response to operation of the position control lever; a position feedback rod located outside the case and configured to be displaceable in response to relative rotation of the lift arm; and a position control transmission mechanism that, when the position control lever is operated, transmits the displacement of the position control lever toward the spool and displaces the position of the spool toward the side that allows supply and discharge of the hydraulic oil, and, when the lift arm rotates relatively, transmits the displacement of the position feedback rod toward the spool and displaces the position of the spool toward the side that restricts supply and discharge of the hydraulic oil.The position control transmission mechanism includes a first position control shaft that rotates about its axis in response to displacement of the position control lever when the position control lever is operated; a second position control shaft that is located higher than the first position control shaft in the lifting / lowering direction of the object and that rotates about its axis in response to displacement of the position feedback rod when the lift arm rotates relatively; and a position control cam that, when the first position control shaft rotates, displaces the position of the spool toward the side that allows supply and discharge of the hydraulic oil in response to the rotation of the first position control shaft, and displaces the position of the spool toward the side that restricts supply and discharge of the hydraulic oil in response to the rotation of the second position control shaft, when the second position control shaft rotates.

[0008] In the hydraulic lifting device, the position control lever has defined one end and the other end, the one end being operable by the operator, and is configured to rotate relatively to the case with the other end as a fulcrum in response to the operation, and the first position control shaft comprises: a co-direction rotation shaft connected to the other end of the position control lever and configured to rotate in the same direction as the rotation direction of the position control lever; a counter-direction rotation shaft connected to the position control cam and configured to rotate in the direction opposite to the rotation direction of the position control lever; and a rotation transmission unit that transmits the rotation of the co-direction rotation shaft to the counter-direction rotation shaft when the position control lever rotates relatively, and rotates the counter-direction rotation shaft in the direction opposite to the rotation direction of the co-direction rotation shaft.

[0009] The hydraulic lifting device further includes a pump lever located outside the case and configured to be displaceable from a first position, which is an arbitrary position when the control valve regulates the supply and discharge of the hydraulic oil, to a second position different from the first position in response to operation by an operator; and a pump transmission mechanism that, when the pump lever is operated to displace from the first position to the second position, transmits the displacement of the pump lever toward the spool and displaces the position of the spool toward the side that allows the supply and discharge of the hydraulic oil, and when the lift arm rotates relatively while the pump lever is located at the second position, transmits the displacement of the position feedback rod toward the spool and displaces the position of the spool toward the side that regulates the supply and discharge of the hydraulic oil. The pump transmission mechanism includes a pump shaft that rotates about its axis in response to the displacement of the pump lever when the pump lever is operated to displace it from the first position to the second position, and a pump cam that displaces the position of the spool toward the side that allows the supply and discharge of the hydraulic oil in response to the rotation of the pump shaft when the pump shaft rotates, and displaces the position of the spool toward the side that restricts the supply and discharge of the hydraulic oil in response to the rotation of the second position control shaft when the second position control shaft rotates.

[0010] In the hydraulic lifting device, the pump lever has one end and the other end defined, and the one end is configured to be operable by the operator, and is configured to be rotatable relative to the case with the other end as a fulcrum in response to the operation, and is provided with a rotation regulating section that regulates the relative rotation of the pump lever.

[0011] The hydraulic lifting device further includes a bracket located outside the case and having one end and the other end defined, the one end being connectable to an object and rotating relative to the case around the other end as a fulcrum in response to a tractive load from the connected object; a draft control lever located outside the case and displaceable in response to operation by an operator; a draft feedback rod located outside the case and displaceable in response to the relative rotation of the bracket; and a draft control transmission mechanism that, when the draft control lever is operated, transmits the displacement of the draft control lever toward the spool and displaces the position of the spool toward the side that allows supply and discharge of the hydraulic oil, and, when the bracket rotates relatively, transmits the displacement of the draft feedback rod toward the spool and displaces the position of the spool toward the side that restricts supply and discharge of the hydraulic oil. The draft control transmission mechanism includes a first draft control shaft that rotates about its axis in response to displacement of the draft control lever when the draft control lever is operated; a second draft control shaft that is located higher than the first draft control shaft in the lifting / lowering direction of the object and that rotates about its axis in response to displacement of the draft feedback rod when the bracket rotates relative to the first draft control shaft; and a draft control cam that displaces the position of the spool toward a side that allows supply and discharge of the hydraulic oil in response to the rotation of the first draft control shaft when the first draft control shaft rotates, and displaces the position of the spool toward a side that restricts supply and discharge of the hydraulic oil in response to the rotation of the second draft control shaft when the second draft control shaft rotates.

[0012] In the hydraulic lifting device, either the first position control shaft or the first draft control shaft has a hollow structure and is configured so that one can be coaxially fitted into the other, and either the second position control shaft or the second draft control shaft has a hollow structure and is configured so that one can be coaxially fitted into the other, and the position control transmission mechanism and the draft control transmission mechanism are configured so that one of the first position control shaft and the first draft control shaft is coaxially fitted into the other, and one of the second position control shaft and the second draft control shaft is coaxially fitted into the other, so that the first position control shaft and the first draft control shaft rotate relatively to each other about their axes in response to displacement of either the position control lever or the draft control lever, and so that the second position control shaft and the second draft control shaft rotate relatively to each other about their axes in response to displacement of either the position feedback rod or the draft feedback rod. [Effects of the Invention]

[0013] According to the present invention, the height of the lift arm in the lifting direction can be easily adjusted to a target height, and the degree of freedom in the layout of component parts can be increased. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an overall perspective view of a hydraulic lifting device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a right side view of the hydraulic lifting device shown in FIG. [Figure 3] FIG. 2 is a left side view of the hydraulic lifting device shown in FIG. [Figure 4] FIG. 2 is a bottom view of the hydraulic lifting device shown in FIG. [Figure 5] 2 is a perspective view showing a part of a drive system inside a case of the hydraulic lifting device shown in FIG. 1. FIG. [Figure 6] 2 is a perspective view showing a part of a drive system inside a case of the hydraulic lifting device shown in FIG. 1. FIG. [Figure 7] FIG. 2 is an overall perspective view of each transmission mechanism in the hydraulic lifting device shown in FIG. [Figure 8] 2 is an enlarged view of a main part showing the positional relationship between each cam and spool in the hydraulic lifting device shown in FIG. 1. FIG. [Figure 9] FIG. 2 is an overall view of a position control transmission mechanism in the hydraulic lifting device shown in FIG. [Figure 10] FIG. 2 is an overall view of a pump transmission mechanism in the hydraulic lifting device shown in FIG. [Figure 11] FIG. 2 is an overall view of a draft control transmission mechanism in the hydraulic lifting device shown in FIG. [Figure 12] 2 is an overall schematic view showing the positional relationship of components of each transmission mechanism in the hydraulic lifting device shown in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] <Overall configuration of hydraulic lifting device> Figure 1 is an overall perspective view of a hydraulic lifting device 100 according to an embodiment of the present invention. Figures 2 and 3 are side views of the hydraulic lifting device 100. Figure 4 is a bottom view of the hydraulic lifting device 100. Arrows indicating left and right, up and down, and front and rear as appropriate in each figure correspond to the leftward and rightward directions, the upward and downward directions, and the forward and rearward directions, respectively.

[0017] The hydraulic lifting device 100 is mounted on an agricultural vehicle such as a tractor. More specifically, the hydraulic lifting device 100 is mounted on the rear of the tractor or the like, above the transmission case. One end 21 of the lift arm 2 and one end 31 of the bracket 3 protrude rearward from the mounted hydraulic lifting device 100. One end 21 of the lift arm 2 is connected to a lower link via a lift link. An end of a top link is connected to one end 31 of the bracket 3. An implement is connected to the rear of the top link and the lower link. As the lift arm 2 rotates relative to the case 1, the connected implement can be raised and lowered in the vertical direction relative to the agricultural vehicle via the top link and lower link.

[0018] 1 to 4, the hydraulic lifting device 100 includes a case 1, a lift arm 2, a bracket 3, a hydraulic cylinder 4, a control valve 5, a position control lever 6, a pump lever 7, a draft control lever 8, a position feedback rod 9, and a draft feedback rod 10. The hydraulic lifting device 100 also includes a position control transmission mechanism 20, a pump transmission mechanism 30, and a draft control transmission mechanism 40. Each of the transmission mechanisms 20, 30, and 40 will be described in detail later.

[0019] The case 1 is a housing, and its bottom is open. Two lift arms 2 are located on the outside rear of the case 1, one on each of the left and right sides. Each lift arm 2 has one end 21 and another end 22. The one end 21 is configured to be connectable to a lift link (not shown). The other end 22 is journaled at both ends of a shaft 23 that penetrates both the left and right sides from inside the case 1 (see Figures 5 and 6). Each lift arm 2 protrudes rearward from the other end 22 toward the one end 21. When the hydraulic cylinder 4 is driven, each lift arm 2 rotates relative to the case 1, with the other end 22 as a fulcrum. In other words, the one end 21 can swing up and down, with the other end 22 as a fulcrum.

[0020] The bracket 3 is located outside the case 1 and rearward of the other end 22 of the lift arm 2. The bracket 3 defines one end 31 and the other end 32. The one end 31 is configured to be connectable to a top link (not shown). The other end 32 is supported by a shaft 33 connected to the case 1 at both ends (see FIGS. 5 and 6). The shaft 33 has, for example, a torsion bar structure, and generates a biasing force in the opposite rotational direction to a rotational load around the shaft. The axis of the shaft 33 is located rearward and below the axis of the shaft 23. The bracket 3 protrudes obliquely downward and rearward from the other end 32 toward the one end 31. The connection portion of the bracket 3 to the top link is located lower than both the shafts 23 and 33. The bracket 3 rotates relative to the case 1, with the other end 32 as a fulcrum, in response to a traction load from the connected top link (i.e., an implement). That is, the one end 31 is biased and can swing back and forth with the other end 32 as a fulcrum.

[0021] 5 and 6 show part of the drive system inside the case 1. As shown in FIGS. 4 to 6, the hydraulic cylinder 4 is connected to a hydraulic oil circuit (not shown) and is driven in response to the supply and discharge of the hydraulic oil. The hydraulic cylinder 4 includes a piston 41 and a piston rod 42 therein. The piston 41 and the piston rod 42 move relative to the case 1 in the front-to-rear direction in response to the supply and discharge of hydraulic oil inside the hydraulic cylinder 4. In the internal space of the case 1, the rear end of the piston rod 42 is connected to the rotation tip end of a crank arm 43. The rotation fulcrum side of the crank arm 43 is connected to the center of the shaft 23 in the left-to-right direction. As a result, the relative movement of the piston 41 and the piston rod 42 in the front-to-rear direction is converted into rotation of the shaft 23.

[0022] 4, the hydraulic cylinder 4 is disposed in the internal space of the case 1 so that the axes of the piston 41 and piston rod 42 are aligned in the front-rear direction and are positioned toward the front left side. Portions of the transmission mechanisms 20, 30, and 40 (described later) are accommodated between the hydraulic cylinder 4 and the upper and right inner walls of the case 1. In addition, a hydraulic oil control valve 5 is accommodated between the hydraulic cylinder 4 and the right inner wall of the case 1.

[0023] The control valve 5 has a hydraulic oil flow path formed therein and is interposed in the hydraulic oil circuit. Other components connected to and interposed in the circuit include a hydraulic pump, a relief valve, a flow path switching valve, a safety valve, and a drop adjustment valve. These components are configured as either one with the case 1 or as separate components. The control valve 5 is located to the right of the hydraulic cylinder 4 in the internal space of the case 1. The control valve 5 has a spool 51 in the hydraulic oil flow path. A front end 51a of the spool 51 is exposed outside the hydraulic oil flow path of the control valve 5. The spool 51 is displaceable in the front-to-rear direction relative to the housing of the control valve 5. The spool 51 is constantly biased forward by a spring.

[0024] The front end 51a of the spool 51 is pressed rearward against the biasing force by the cams of the transmission mechanisms 20, 30, and 40. At this time, the position of the spool 51 is displaced rearward, allowing the supply of hydraulic oil to the hydraulic cylinder 4. When hydraulic oil is supplied to the hydraulic cylinder 4, the piston 41 and the piston rod 42 are displaced, and the lift arm 2 rotates relative to the hydraulic cylinder 4 via the crank arm 43 and the shaft 23. On the other hand, when the pressure from the cams of the transmission mechanisms 20, 30, and 40 is released, the position of the spool 51 is displaced forward along the biasing force, restricting the supply of hydraulic oil to the hydraulic cylinder 4. As a result, the displacement of the piston 41 and the piston rod 42 and the rotation of the crank arm 43 and the shaft 23 are restricted, and the position (height) of the lift arm 2, which had been rotating relatively, is fixed.

[0025] As shown in FIGS. 1 and 2, the position control lever 6, pump lever 7, and draft control lever 8 are located outside the case 1 on the right side, and are each located forward of the lift arm 2. The position control lever 6 has one end 61 and another end 62. The one end 61 is configured to be operable by an operator. The other end 62 is pivotally supported by the right end of a first position control shaft 220 that penetrates the right side surface from inside the case 1 (see FIGS. 7 and 9). The position control lever 6 protrudes upward from the other end 62 toward the one end 61. When the one end 61 is operated by an operator, the position control lever 6 rotates relative to the case 1 with the other end 62 as a fulcrum, as a displacement corresponding to the operation. In other words, the one end 61 can swing back and forth with the other end 62 as a fulcrum.

[0026] The pump lever 7 has one end 71 and another end 72. The one end 71 is configured to be operable by an operator. A grip (not shown) that can be held by the operator may be provided separately. The other end 72 is pivotally supported by the right end of a pump shaft 320 that penetrates the right side surface from inside the case 1 (see FIGS. 7 and 10). The pump lever 7 protrudes upward from the other end 72 toward the one end 71. The other end 72 of the pump lever 7 is located higher than the other end 62 of the position control lever 6. When the one end 71 of the pump lever 7 is operated by an operator, the pump lever 7 rotates relative to the case 1 with the other end 72 as a fulcrum, as a displacement corresponding to the operation. In other words, the one end 71 can swing back and forth with the other end 72 as a fulcrum. More specifically, the pump lever 7 is configured to be displaceable from a first position, which is an arbitrary position when the supply and discharge of hydraulic oil is regulated by the control valve 5, to a second position different from the first position in response to operation by the operator.

[0027] Here, the "state in which the supply and discharge of hydraulic oil is restricted by the control valve 5" refers to, for example, a state after the position of the spool 51 has been displaced toward the restricting side of the supply and discharge of hydraulic oil due to displacement of the position feedback rod 9. The relationship between the "first position" and the "second position" is such that the positions of the one end side 71 are different from each other. For example, the one end side 71 in the second position may be located forward or rearward of the one end side 71 in the first position. The movement of the one end side 71 displaces the position of the spool 51 toward the allowing side of the supply and discharge of hydraulic oil.

[0028] The pump lever 7 has a detent mechanism to prevent relative rotation. In this embodiment, the detent mechanism functions only when the pump lever 7 is lowered. However, it may also function when the pump lever 7 is raised. In addition to the detent mechanism, the pump lever 7 also has a rotation restricting portion 74 that restricts the relative rotation of the pump lever 7. The rotation restricting portion 74 may be indirectly fixed to the case 1 via, for example, a plate 73 provided on the case 1. The rotation restricting portion 74 has a protruding member 74a that protrudes forward. The protruding member 74a is located rearward of the pump lever 7, and the front end of the protruding member 74a can intersect with the radial path of the pump lever 7. Therefore, when the one end side 71 continues to swing rearward, the pump lever 7, which rotates counterclockwise in FIG. 2 , eventually abuts against the front end of the protruding member 74a. At this time, the relative rotation of the pump lever 7 is restricted. As a result of the restriction of relative rotation, the elevation height of the connected implement can be easily adjusted to any desired position.

[0029] The position of the front end of the protruding member 74a can be adjusted in the front-rear direction by a length adjustment mechanism such as a screw. That is, the position where the pump lever 7 abuts against the protruding member 74a can also be adjusted in the front-rear direction. Therefore, the relative rotation of the pump lever 7 is restricted further forward as the position of the front end of the protruding member 74a is displaced forward.

[0030] The draft control lever 8 has one end 81 and another end 82. The one end 81 is configured to be operable by an operator. The other end 82 is pivotally supported by the right end of a first draft control shaft 420 that penetrates the right side surface from inside the case 1 (see FIGS. 7 and 11). The draft control lever 8 protrudes upward from the other end 82 toward the one end 81. The other end 82 of the draft control lever 8 is positioned coaxially with the other end 62 of the position control lever 6. The draft control lever 8 is positioned adjacent to the left of the position control lever 6. When the one end 81 of the draft control lever 8 is operated by an operator, the draft control lever 8 rotates relative to the case 1 with the other end 82 as a fulcrum, as a displacement corresponding to the operation. In other words, the one end 81 can swing back and forth with the other end 82 as a fulcrum.

[0031] As shown in Figures 3 to 6, the position feedback rod 9 and the draft feedback rod 10 are located outside the case 1 on the left side, and each extends in the front-to-rear direction. The rear end 91 of the position feedback rod 9 is connected to the lower end of the cam 24 so as to be able to rotate relatively. The cam 24 is fixed coaxially to the shaft 23 of the left lift arm 2 and protrudes downward. When the lift arm 2 rotates relative to the case 1, the cam 24 also rotates integrally, and the lower end of the cam 24 swings in the front-to-rear direction. In response to this, the position feedback rod 9 is able to displace in the front-to-rear direction.

[0032] A front end 92 of the position feedback rod 9 is connected to the lower end of cam 230a so as to be rotatable relative to the cam. Cam 230a is journaled at the left end of second position control shaft 230, which penetrates the left side surface from inside the case 1, and protrudes downward (see FIGS. 7 and 9). When the position feedback rod 9 is displaced in the front-rear direction, the lower end of cam 230a swings in the front-rear direction, allowing second position control shaft 230 to rotate relatively.

[0033] The rear end side 101 of the draft feedback rod 10 is connected to the lower end of the joint 34. The joint 34 is fixed integrally to the left side surface of the bracket 3 and protrudes downward to the left. When the bracket 3 rotates relative to the case 1, the joint 34 also rotates integrally, and the lower end of the joint 34 swings in the front-to-rear direction. In response to this, the draft feedback rod 10 is capable of displacement in the front-to-rear direction.

[0034] The front end side 102 of the draft feedback rod 10 is connected to the lower end of the cam 430a so as to be rotatable relative to the second draft control shaft 430. A portion of the front end side 102 is formed by a spring 102a. The cam 430a is journaled at the left end of a second draft control shaft 430, which penetrates the left side surface from inside the case 1, and protrudes downward to the left (see FIGS. 7 and 11). The connection position of the front end side 102 with the cam 430a is higher than the connection position of the front end side 92 of the position feedback rod 9 with the cam 230a. When the draft feedback rod 10 is displaced in the front-rear direction, the lower end of the cam 430a swings in the front-rear direction, allowing the second draft control shaft 430 to rotate relatively. In particular, when the draft feedback rod 10 is displaced forward, the spring 102a shrinks slightly from its attached length, and the cam 430a swings forward while being biased by the spring 102a. On the other hand, when the draft feedback rod 10 is displaced rearward, the spring 102a does not interfere (does not extend).

[0035] <Transmission mechanism configuration> 7 to 12, the hydraulic lifting device 100 includes a position control transmission mechanism 20, a pumper transmission mechanism 30, and a draft control transmission mechanism 40. Each transmission mechanism 20, 30, 40 is configured to transmit the displacement of each lever 6, 7, 8 and the displacement of each rod 9, 10 toward the spool 51 of the control valve 5. The displacements input to each transmission mechanism 20, 30, 40 are ultimately collected into the position control cam 210, the pumper cam 310, and the draft control cam 410, and displace each of the cams 210, 310, 410, respectively.

[0036] FIG. 8 is an enlarged view of essential parts showing the positional relationship of the cams 210, 310, and 410 and the spool 51 inside the case 1. As shown in FIG. 8, the position control cam 210, the pumper cam 310, and the draft control cam 410 each have a roughly "E" shape when viewed from the left side. From left to right, the draft control cam 410, the position control cam 210, and the pumper cam 310 are arranged in this order, overlapping each other with a gap between them. Each cam 210, 310, and 410 is provided with a pin that penetrates approximately the center in the vertical direction in the left-right direction for positioning. The cams 210, 310, and 410 are capable of relative rotation around the pin. The position control cam 210, the pump cam 310, and the draft control cam 410 are displaced such that the upper end sides 212, 312, 412 or the lower end sides 213, 313, 413 thereof can swing in the front-rear direction.

[0037] In response to this swing, the respective protrusions 211, 311, 411 can swing integrally in the front-to-rear direction. When the protrusions 211, 311, 411 swing and displace rearward, the front end 51a of the spool 51 is pressed by the protrusions 211, 311, 411 and displaced rearward. Next, when the protrusions 211, 311, 411 swing and displace forward, the spool 51 is displaced forward in response to the biasing force of the spring. In this way, the spool 51 of the control valve 5 is also displaced in response to the respective displacements of the respective cams 210, 310, 410. The specific operation of the respective cams 210, 310, 410 will be described together with the detailed description of the respective transmission mechanisms 20, 30, 40.

[0038] The configurations of the position control transmission mechanism 20, the pumper transmission mechanism 30, and the draft control transmission mechanism 40 will be described in detail below.

[0039] <<Position control transmission mechanism>> 9 is an overall view of the position control transmission mechanism 20. As shown in FIG. 9, the position control transmission mechanism 20 includes a position control cam 210, a first position control shaft 220, and a second position control shaft 230.

[0040] The first position control shaft 220 includes a co-directional rotation shaft 221, a counter-directional rotation shaft 222, and a rotation transmission unit 223. The co-directional rotation shaft 221 extends in the left-right direction and has an axis A1 that is parallel to the left-right direction. The right end of the co-directional rotation shaft 221 is connected to the other end 62 of the position control lever 6. The co-directional rotation shaft 221 is rotatable around the axis A1 in the same direction as the rotation of the position control lever 6. A cam 221a that protrudes upward is provided on the left end of the co-directional rotation shaft 221. The cam 221a is oscillatable in the front-rear direction in response to the rotation of the co-directional rotation shaft 221 around the axis A1.

[0041] The reverse-direction-rotation shaft 222 extends in the left-right direction and has an axis A2 that is parallel to the left-right direction. Axis A2 is located diagonally above and forward of axis A1. That is, the same-direction-rotation shaft 221 and the reverse-direction-rotation shaft 222 are arranged to have different axes. As shown in the dashed line in FIG. 9 and in FIG. 12, the reverse-direction-rotation shaft 222 has a hollow structure along axis A2, and the reverse-direction-rotation shaft 422 of the first draft control shaft 420 can be coaxially inserted into the hollow structure.

[0042] A downwardly protruding cam 222a is provided on the right end of the reverse rotation shaft 222. In response to the forward and backward swing of the cam 222a, the reverse rotation shaft 222 can rotate around axis A2 in the direction opposite to the rotation direction of the position control lever 6. A downwardly protruding cam 222b is provided on the left end of the reverse rotation shaft 222. The cam 222b can swing forward and backward in response to the rotation of the reverse rotation shaft 222 about axis A2.

[0043] The rotation transmitting part 223 is a plate extending in the front-rear direction. The rear side of the rotation transmitting part 223 is rotatably connected to the upper end of the cam 221a, and the front side of the rotation transmitting part 223 is rotatably connected to the lower end of the cam 222a. The rotation transmitting part 223 swings the cam 222a in the front-rear direction in response to the swinging of the cam 221a in the front-rear direction.

[0044] In the first position control shaft 220 configured as described above, when the position control lever 6 is operated, the same-direction rotation shaft 221 rotates about axis A1 and the reverse-direction rotation shaft 222 rotates about axis A2 in accordance with the displacement of the position control lever 6. More specifically, when the position control lever 6 and the same-direction rotation shaft 221 each rotate in direction R1 due to operation of the position control lever 6, the cam 221a swings forward. Direction R1 corresponds to the clockwise direction when viewed from right to left. In response to the forward swing of the cam 221a, the cam 222a also swings forward via the rotation transmission part 223. In response to the forward swing of the cam 222a, the reverse-direction rotation shaft 222 rotates in direction R2, which is opposite to direction R1. Direction R2 corresponds to the counterclockwise direction when viewed from right to left.

[0045] On the other hand, when the position control lever 6 is operated to rotate the position control lever 6 and the same-direction rotation shaft 221 in direction R2, the cam 221a swings rearward. In response to the rearward swing of the cam 221a, the cam 222a also swings rearward via the rotation transmission unit 223. In response to the rearward swing of the cam 222a, the reverse-direction rotation shaft 222 rotates in direction R1, which is opposite to direction R2. In other words, the rotation transmission unit 223 transmits the rotation of the same-direction rotation shaft 221 to the reverse-direction rotation shaft 222, and rotates the reverse-direction rotation shaft 222 in the direction opposite to the rotation direction of the same-direction rotation shaft 221.

[0046] The second position control shaft 230 extends in the left-right direction and has an axis A3 that is parallel to the left-right direction. The axis A3 is located above the axis A2. In other words, the first position control shaft 220 and the second position control shaft 230 are arranged to have different axes, and the second position control shaft 230 is located above the first position control shaft 220.

[0047] A downward-protruding cam 230a is provided on the left end of the second position control shaft 230. The front end 92 of the position feedback rod 9 is connected to the lower end of the cam 230a so as to be relatively rotatable. In response to the forward and backward swing of the cam 230a, the second position control shaft 230 is rotatable around the axis A3.

[0048] An upward-protruding cam 230b is provided slightly to the right of the center in the left-right direction of the second position control shaft 230. The cam 230b is able to swing back and forth in response to the rotation of the second position control shaft 230 about the axis A3. An extension 231 of the same diameter is provided on the right end side of the second position control shaft 230. The extension 231 extends rightward from the cam 230b coaxially with the axis A3.

[0049] The second position control shaft 230 configured in this manner rotates around axis A3 in response to the displacement of the position feedback rod 9 when the lift arm 2 rotates relative to the lift arm 2. More specifically, when the cam 24 swings rearward due to the lift arm 2 swinging upward, the position feedback rod 9 is displaced rearward. In response to the rearward displacement of the position feedback rod 9, the cam 230a swings rearward. In response to the rearward swing of the cam 230a, the second position control shaft 230 rotates in direction R1.

[0050] On the other hand, when the cam 24 swings forward due to the downward swing of the lift arm 2, the position feedback rod 9 is displaced forward. In response to the forward displacement of the position feedback rod 9, the cam 230a swings forward. In response to the forward swing of the cam 230a, the second position control shaft 230 rotates in direction R2, which is opposite to direction R1.

[0051] The position control cam 210 is defined by a protruding portion 211, an upper end side 212, and a lower end side 213. The protruding portion 211 protrudes rearward from approximately the center in the up-down direction and is capable of abutting against the front end side 51a of the spool 51, as described above. The upper end side 212 is connected to the cam 230b of the second position control shaft 230 so as to be able to rotate relative to the cam 230b. The lower end side 213 is connected to the cam 222b of the reverse direction rotation shaft 222 (first position control shaft 220) so as to be able to rotate relative to the cam 222b.

[0052] When the position control lever 6 is operated, the position control lever 6 and the same-direction rotation shaft 221 each rotate in direction R2, and the reverse-direction rotation shaft 222 rotates in direction R1, causing the cam 222b to swing rearward. In response to the rearward swing of the cam 222b, the lower end 213 of the position control cam 210 also swings rearward, and the protrusion 211 is also displaced rearward. As a result, the spool 51 is displaced toward the side that allows the supply and discharge of hydraulic oil (i.e., the rearward side). This displacement of the spool 51 causes the lift arm 2 to swing upward.

[0053] Next, as the lift arm 2 swings upward, the second position control shaft 230 rotates in direction R1, causing the cam 230b to swing forward. In response to the forward swing of the cam 230b, the upper end 212 of the position control cam 210 also swings forward, and the protrusion 211 is also displaced forward. This causes the spool 51 to displace toward the side where the supply and discharge of hydraulic oil is regulated (i.e., toward the front). This displacement of the spool 51 stops the lift arm 2, which is swinging upward.

[0054] <<Pumper transmission mechanism>> 10 is an overall view of the pump transmission mechanism 30. As shown in FIG.

[0055] The pumper shaft 320 extends in the left-right direction and is disposed coaxially with the axis A3. As shown in the dashed line in Fig. 10 and in Fig. 12, the pumper shaft 320 has a hollow structure along the axis A3, and the extension portion 231 of the second position control shaft 230 can be coaxially inserted into the pumper shaft 320.

[0056] The right end of the pumper shaft 320 is connected to the other end 72 of the pumper lever 7. The pumper shaft 320 is rotatable around an axis A3 in the same direction as the rotation of the pumper lever 7. A cam 320a that protrudes downward is provided on the left end of the pumper shaft 320. The cam 320a is oscillatable back and forth in response to the rotation of the pumper shaft 320 around the axis A3.

[0057] The rotation transmitting unit 330 is a plate extending in the vertical direction and is disposed coaxially with the axis A2. As shown in the dashed line in FIG. 10 and in FIG. 12, the rotation transmitting unit 330 has a mating hole along the axis A2, into which the reverse rotation shaft 222 of the first position control shaft 220 can be coaxially fitted. The upper side of the rotation transmitting unit 330 is rotatably connected to the lower end of the cam 320a, and the lower side of the rotation transmitting unit 330 is rotatably connected to the lower end 313 of the pumper cam 310. The rotation transmitting unit 330 swings the lower end 313 in the longitudinal direction in response to the longitudinal swing of the cam 320a.

[0058] When the pump lever 7 is operated, the pump shaft 320 configured in this manner rotates around the axis A3 in response to the displacement of the pump lever 7. More specifically, when the pump shaft 320 rotates in direction R1 due to the operation of the pump lever 7, the cam 320a swings rearward. In response to the rearward swing of the cam 320a, the rotation transmission part 330 rotates in direction R2, which is opposite to direction R1.

[0059] On the other hand, when the pump lever 7 and the pump shaft 320 are rotated in the direction R2 by operating the pump lever 7, the cam 320a swings forward. In response to the swinging of the cam 320a forward, the rotation transmission part 330 rotates in the direction R1 opposite to the direction R2.

[0060] The pumper cam 310 has a protruding portion 311, an upper end side 312, and a lower end side 313. The protruding portion 311 protrudes rearward from approximately the center in the up-down direction and is capable of abutting against the front end side 51a of the spool 51, as described above. The upper end side 312 is connected to the cam 230b of the second position control shaft 230 so as to be rotatable relative to the cam 230b. More specifically, as shown in FIG. 12 , the upper end side 312 is interposed between the cam 230b and the upper end side 212 of the position control cam 210. The cam 230b and the upper end sides 312, 212 are pinned so that the upper end sides 312, 212 can swing integrally in response to the swing of the cam 230b. The lower end side 313 is connected to the lower side of the rotation transmission part 330 so as to be rotatable relative to the cam 230b.

[0061] With the supply and discharge of hydraulic oil restricted by the control valve 5, the pump lever 7 is moved from the first position to the second position. When the pump lever 7 and the pump shaft 320 are rotated in the direction R2 by operating the pump lever 7, the cam 320a swings forward, and the rotation transmission unit 330 rotates in the direction R1. In response to the rotation of the rotation transmission unit 330 in the direction R1, the lower end 313 of the pump cam 310 also swings rearward, and the protrusion 211 also moves rearward. As a result, the spool 51 moves toward the side where the supply and discharge of hydraulic oil is permitted (i.e., the rearward side). In response to the displacement of the spool 51, the lift arm 2 swings upward.

[0062] Next, as the lift arm 2 swings upward, the second position control shaft 230 rotates in direction R1, causing the cam 230b to swing forward. In response to the swinging forward of the cam 230b, the upper end 312 of the pumper cam 310 swings forward together with the upper end 212 of the position control cam 210, and the protrusion 311 also moves forward. This causes the spool 51 to move toward the hydraulic oil supply / discharge restriction side (i.e., the front side). In response to the displacement of the spool 51, the lift arm 2, which had been swinging upward, stops.

[0063] <<Draft control transmission mechanism>> 11 is an overall view of the draft control transmission mechanism 40. As shown in FIG. 11, the draft control transmission mechanism 40 includes a draft control cam 410, a first draft control shaft 420, and a second draft control shaft 430.

[0064] The first draft control shaft 420 includes a co-directional rotation shaft 421, a counter-directional rotation shaft 422, and a rotation transmission unit 423. The co-directional rotation shaft 421 extends in the left-right direction and is disposed coaxially with the axis A1. As shown in the dashed line in FIG. 11 and in FIG. 12, the co-directional rotation shaft 421 has a hollow structure along the axis A1, and the co-directional rotation shaft 221 of the first position control shaft 220 can be coaxially inserted therein. The right end of the co-directional rotation shaft 421 is connected to the other end 82 of the draft control lever 8. The co-directional rotation shaft 421 is rotatable around the axis A1 in the same direction as the rotation of the draft control lever 8. A cam 421a protruding upward is provided on the left end of the co-directional rotation shaft 421, adjacent to the right side of the cam 221a. The cam 421a is oscillatable back and forth in response to the rotation of the co-directional rotation shaft 421 around the axis A1. Each of the oscillating cams 421a, 221a can come into contact with the stay. When the cams 421a, 221a come into contact with the stay, the oscillation of the cams 421a, 221a is restricted, and the operation of the levers 6, 8 is also restricted. That is, by adjusting the contact position between the cams 421a, 221a and the stay, the operating range of each of the levers 6, 8 can be set. For example, in this embodiment, the operating range may be set so that the operating angle of each of the levers 6, 8 is 45 degrees.

[0065] The reverse-direction rotation shaft 422 extends in the left-right direction and is arranged coaxially with the axis A2. That is, the same-direction rotation shaft 421 and the reverse-direction rotation shaft 422 are arranged to have different axes. As shown in the dashed line in FIG. 11 and in FIG. 12, the reverse-direction rotation shaft 422 is fitted inside the reverse-direction rotation shaft 222 of the first position control shaft 220.

[0066] A downwardly protruding cam 422a is provided on the right end of the reverse-direction rotation shaft 422 so as to be adjacent to the right side of the cam 222a. In response to the forward and backward swing of the cam 422a, the reverse-direction rotation shaft 422 can rotate around the axis A2 in the direction opposite to the rotation direction of the draft control lever 8. A downwardly protruding cam 422b is provided on the left end of the reverse-direction rotation shaft 422. The cam 422b can swing forward and backward in response to the rotation of the reverse-direction rotation shaft 422 about the axis A2.

[0067] The rotation transmitting part 423 is a plate extending in the front-rear direction and adjacent to the right side of the rotation transmitting part 223. The rear side of the rotation transmitting part 423 is rotatably connected to the upper end of the cam 421a, and the front side of the rotation transmitting part 423 is rotatably connected to the lower end of the cam 422a. The rotation transmitting part 423 swings the cam 422a in the front-rear direction in response to the swinging of the cam 421a in the front-rear direction.

[0068] In the first draft control shaft 420 configured as described above, when the draft control lever 8 is operated, the same-direction rotation shaft 421 rotates about axis A1 and the reverse-direction rotation shaft 422 rotates about axis A2 in accordance with the displacement of the draft control lever 8. More specifically, when the draft control lever 8 and the same-direction rotation shaft 421 each rotate in direction R1 by operating the draft control lever 8, the cam 421a swings forward. In response to the forward swing of the cam 421a, the cam 422a also swings forward via the rotation transmission part 423. In response to the forward swing of the cam 422a, the reverse-direction rotation shaft 422 rotates in direction R2 opposite to direction R1.

[0069] On the other hand, when the draft control lever 8 and the same-direction rotation shaft 421 each rotate in direction R2 by operating the draft control lever 8, the cam 421a swings rearward. In response to the rearward swing of the cam 421a, the cam 422a also swings rearward via the rotation transmission unit 423. In response to the rearward swing of the cam 422a, the reverse-direction rotation shaft 422 rotates in direction R1 opposite to direction R2. In other words, the rotation transmission unit 423 transmits the rotation of the same-direction rotation shaft 421 to the reverse-direction rotation shaft 422, and rotates the reverse-direction rotation shaft 422 in the direction opposite to the rotation direction of the same-direction rotation shaft 421.

[0070] The second draft control shaft 430 extends in the left-right direction and is disposed coaxially with the axis A3. As shown in the dashed line portion of Fig. 11 and in Fig. 12, the second draft control shaft 430 has a hollow structure along the axis A3, and the second position control shaft 230 can be coaxially inserted therein. In other words, the first draft control shaft 420 and the second draft control shaft 430 are disposed to have different axes, and the second draft control shaft 430 is located above the first draft control shaft 420.

[0071] A cam 430a protruding downward is provided on the left end of the second draft control shaft 430. The front end 102 of the draft feedback rod 10 is connected to the lower end of the cam 430a so as to be relatively rotatable. The second draft control shaft 430 is rotatable around an axis A3 in response to the forward and backward swing of the cam 430a.

[0072] An upwardly protruding cam 430b is provided on the right end side of the second draft control shaft 430. The cam 430b is capable of swinging back and forth in response to the rotation of the second draft control shaft 430 about the axis A3.

[0073] The second draft control shaft 430 configured in this manner rotates around the axis A3 in response to the displacement of the draft feedback rod 10 when the bracket 3 rotates relative to the bracket 3. More specifically, when the joint 34 swings rearward due to the bracket 3 swinging rearward, the spring 102a does not extend beyond its mounting length, and the draft feedback rod 10 is displaced rearward. In response to the rearward displacement of the draft feedback rod 10, the cam 430a swings rearward. In response to the rearward swing of the cam 430a, the second draft control shaft 430 rotates in direction R1.

[0074] On the other hand, when the bracket 3 swings forward, causing the joint 34 to swing forward, the draft feedback rod 10 is displaced forward. In this case, the draft feedback rod 10 is displaced while the spring 102a is slightly compressed from its attached length. In this way, the compression of the spring 102a can suppress hunting caused by input. To appropriately suppress the hunting, for example, the spring constant of the spring 102a may be adjusted. In response to the forward displacement of the draft feedback rod 10, the cam 430a swings forward. In response to the forward swing of the cam 430a, the second draft control shaft 430 rotates in a direction R2 opposite to the direction R1.

[0075] 11 and 12, a protrusion 102b is further provided on the front end 102 of the draft feedback rod 10. The protrusion 102b protrudes to the right and is located above the position feedback rod 9 and behind the cam 230a of the second position control shaft 230. In other words, the protrusion 102b can intersect with the radial locus of the cam 230a.

[0076] For this reason, for example, if the position feedback rod 9 continues to displace rearward, the cam 230a, which rotates relatively rearward, will eventually abut against the protrusion 102b. After the abutment, if the position feedback rod 9 displaces further rearward, the cam 230a presses the protrusion 102b rearward, causing the spring 102a to compress. As a result, the portion of the draft feedback rod 10 rearward of the spring 102a does not displace rearward, and the bracket 3 does not swing. Meanwhile, in conjunction with the protrusion 102b being pressed rearward, the cam 430a also swings rearward, and the second draft control shaft 430 rotates in direction R1.

[0077] The draft control cam 410 is defined by a protruding portion 411, an upper end side 412, and a lower end side 413. The protruding portion 411 protrudes rearward from approximately the center in the up-down direction and is capable of abutting against the front end side 51a of the spool 51, as described above. The upper end side 412 is connected to a cam 430b of the second draft control shaft 430 so as to be able to rotate relative to the cam 430b. The lower end side 413 is connected to a cam 422b of the reverse-direction rotation shaft 422 (first draft control shaft 420) so as to be able to rotate relative to the cam 422b.

[0078] The operation of the draft control lever 8 will be described below. As a prerequisite for operation, assume that a tractive load from the top link (implement) is applied to the bracket 3, the bracket 3 is oscillatingly displaced in response to the tractive load, and the spool 51 is positioned in a neutral position. In this state, when the draft control lever 8 is operated, the draft control lever 8 and the same-direction rotation shaft 421 each rotate in direction R2, and the opposite-direction rotation shaft 422 rotates in direction R1, the cam 422b swings rearward. In response to the rearward swing of the cam 422b, the lower end 413 of the draft control cam 410 also swings rearward, and the protrusion 411 also displaces rearward. As a result, the spool 51 is displaced toward the side that allows the supply and discharge of hydraulic oil (i.e., the rearward side). The displacement of the spool 51 causes the lift arm 2 to swing upward.

[0079] Next, as the lift arm 2 swings upward, the implement connected to the lift arm 2 also moves upward. For example, if the bottom end of the implement penetrates the ground, the tillage depth decreases. On the other hand, if the bottom end of the implement is separated from the ground, the separation distance increases. Therefore, the tractive load from the top link to the bracket 3 changes, and the bracket 3 rotates relative to the top link 3 accordingly. The relative rotation of the bracket 3 causes the second draft control shaft 430 to rotate in direction R1, and the cam 430b to swing forward.

[0080] On the other hand, when the cam 230a presses the protrusion 102b rearward due to the upward swing of the lift arm 2, the spring 102a of the draft feedback rod 10 is compressed. Meanwhile, the cam 430a also swings rearward in conjunction with the protrusion 102b being pressed rearward. In this case, the second draft control shaft 430 also rotates in the direction R1, and the cam 430b swings forward.

[0081] In response to the forward swing of cam 430b, the upper end 412 of draft control cam 410 also swings forward, and protrusion 411 is also displaced forward. This causes spool 51 to displace toward the side where the supply and discharge of hydraulic oil is regulated (i.e., toward the front). The displacement of spool 51 stops the lift arm 2 swinging upward.

[0082] <Effects of the embodiment> As described above, the hydraulic lifting device 100 according to the embodiment of the present invention includes the lift arm 2, the position control lever 6, and the position control transmission mechanism 20. The position control transmission mechanism 20 includes a position control cam 210, a first position control shaft 220, and a second position control shaft 230. When the position control lever 6 is operated, the first position control shaft 220 rotates about axis A1 (and axis A2) in response to the displacement of the position control lever 6. When the lift arm 2 rotates relative to the first position control shaft 220, the second position control shaft 230 rotates about axis A3 in response to the displacement of the position feedback rod 9. When the first position control shaft 220 rotates, the position control cam 210 displaces the position of the spool 51 toward the side that allows the supply and discharge of hydraulic oil in response to the rotation of the first position control shaft 220. When the second position control shaft 230 rotates, the position control cam 210 displaces the position of the spool 51 toward the side that restricts the supply and discharge of hydraulic oil in accordance with the rotation of the second position control shaft 230. This makes it possible to easily adjust the height of the lift arm 2 in the lifting direction toward a desired height.

[0083] The second position control shaft 230 is located above the first position control shaft 220 in the lifting direction of the top link (implement). In this embodiment, the axis A3 of the second position control shaft 230 is located above the axis A1 of the first position control shaft 220. This allows the space below the second position control shaft 230 to be effectively used as a space for accommodating components. For this reason, for example, as shown in FIG. 7, by accommodating the hydraulic cylinder 4 below the second position control shaft 230 and to the left of the first position control shaft 220, the hydraulic lifting device 100 can be made smaller overall. In this way, the degree of freedom in the layout of the components can be increased.

[0084] Therefore, the height of the lift arm 2 in the lifting direction can be easily adjusted to the desired height, and the degree of freedom in the layout of the components can be increased. Furthermore, the hydraulic cylinder 4, which is one of the heaviest components, can be located lower in the internal space of the hydraulic lifting device 100. This allows the position of the center of gravity of the hydraulic lifting device 100 to be adjusted over a wide range.

[0085] Furthermore, particularly in this embodiment, the position control lever 6 has defined one end 61 and the other end 62. The one end 61 is configured to be operable by an operator, and is configured to rotate relative to the case 1 with the other end 62 as a fulcrum, as a displacement in response to the operation. The first position control shaft 220 includes a same-direction rotation shaft 221, a reverse-direction rotation shaft 222, and a rotation transmission unit 223. The same-direction rotation shaft 221 is connected to the other end 62 of the position control lever 6 and is configured to be rotatable in the same direction as the rotation direction of the position control lever 6. The reverse-direction rotation shaft 222 is connected to the position control cam 210 and is configured to be rotatable in the direction opposite to the rotation direction of the position control lever 6. When the position control lever 6 rotates relative to the case 1, the rotation transmission unit 223 transmits the rotation of the same-direction rotation shaft 221 to the reverse-direction rotation shaft 222 and rotates the reverse-direction rotation shaft 222 in the direction opposite to the rotation direction of the same-direction rotation shaft 221.

[0086] This allows the same-direction rotation shaft 221 and the opposite-direction rotation shaft 222 to be arranged with different axes via the rotation transmission unit 223. For example, as shown in FIG. 9, the position of the axis A1 of the same-direction rotation shaft 221 and the position of the axis A2 of the opposite-direction rotation shaft 222 can be made different from each other. This allows the same-direction rotation shaft 221 and the opposite-direction rotation shaft 222 to be laid out without interfering with the placement of the hydraulic cylinder 4, control valve 5, etc. In other words, this increases the degree of freedom in the layout of the first position control shaft 220 and the position control lever 6, allowing, for example, a layout that is easy for the operator to operate. Furthermore, by changing the link ratio in the rotation transmission unit 223, the displacement amount of the position control cam 210 (displacement amount of the spool 51) relative to the displacement amount of the position control lever 6 can be adjusted. This allows the operating range of the position control lever 6 to be adjusted to make it easier for the operator to operate it.

[0087] In this embodiment, the vehicle is particularly equipped with a pump lever 7 and a pump transmission mechanism 30. The pump lever 7 is configured to be displaceable from a first position to a second position in response to operation by the operator. The pump transmission mechanism 30 includes a pump cam 310, a pump shaft 320, and a second position control shaft 230. When the pump lever 7 is operated to displace it from the first position to the second position, the pump shaft 320 rotates about axis A3 in response to the displacement of the pump lever 7. When the pump shaft 7 rotates, the pump cam 310 displaces the position of the spool 51 toward the side that allows the supply and discharge of hydraulic oil in response to the rotation of the pump shaft 7. When the second position control shaft 230 rotates, the pump cam 310 displaces the position of the spool 51 toward the side that restricts the supply and discharge of hydraulic oil in response to the rotation of the second position control shaft 230. This allows the lift arm 2 to be easily raised and lowered according to the operator's request.

[0088] For example, when the rotation transmission unit 330 is provided in the pump transmission mechanism 30 as in this embodiment, the pump shaft 320 and the lower end 313 of the pump cam 310 can be arranged on different axes via the rotation transmission unit 330 (see FIG. 10 ). This allows the pump shaft 320 to be laid out without interfering with the arrangement of the hydraulic cylinder 4, control valve 5, and the like. This increases the degree of freedom in the layout of the pump shaft 320 and pump lever 7, allowing, for example, a layout that is easy for the operator to operate. Furthermore, by changing the link ratio in the rotation transmission unit 330, the displacement amount of the pump cam 310 (displacement amount of the spool 51) relative to the displacement amount of the pump lever 7 can be adjusted. This allows the operating range of the pump lever 7 to be adjusted to make it easier for the operator to operate it.

[0089] In particular, in this embodiment, the pump lever 7 has defined one end 71 and the other end 72. The one end 71 is operable by an operator, and the other end 72 is rotatable relative to the case 1, with the other end 72 serving as a fulcrum, depending on the operation. Furthermore, a rotation restricting unit 74 is provided to restrict the relative rotation of the pump lever 7. This allows the lifting height of the implement by operating the pump lever 7 to be intentionally restricted to any desired position. For example, if the implement is raised too high, the center of gravity also rises, increasing the risk of tipping. This is particularly true when using a relatively heavy implement (e.g., a plow) on sloping ground. In such cases, the lifting height of the implement can be appropriately restricted, improving safety. Meanwhile, restricting the lifting height of the implement to the minimum necessary height shortens the time it takes for the implement to land on the ground, for example, when lowering the implement after a swing during a work interruption. Therefore, the time during which work is interrupted can be reduced, and work efficiency can be improved accordingly.

[0090] In this embodiment, the bracket 3, the draft control lever 8, and the draft control transmission mechanism 40 are particularly provided. The draft control transmission mechanism 40 includes a draft control cam 410, a first draft control shaft 420, and a second draft control shaft 430. When the draft control lever 8 is operated, the first draft control shaft 420 rotates around the axis A1 (and the axis A2) in response to the displacement of the draft control lever 8. When the bracket 3 rotates relative to the bracket 3, the second draft control shaft 430 rotates around the axis A3 in response to the displacement of the draft feedback rod 10. When the first draft control shaft 420 rotates, the draft control cam 410 displaces the position of the spool 51 toward the side that allows the supply and discharge of hydraulic oil in response to the rotation of the first draft control shaft 420. When the second draft control shaft 430 rotates, the draft control cam 410 displaces the position of the spool 51 toward the side that restricts the supply and discharge of hydraulic oil in response to the rotation of the second draft control shaft 430. Therefore, the lift height of the lift arm 2 can be easily adjusted so that the traction load on the bracket 5 reaches a target magnitude.

[0091] The second draft control shaft 430 is located above the first draft control shaft 420 in the lifting direction of the top link (implement). In this embodiment, the axis A3 of the second draft control shaft 430 is located above the axis A1 of the first draft control shaft 420. This allows the space below the second draft control shaft 430 to be effectively used as a space for accommodating components. For this reason, for example, as shown in FIG. 7, by accommodating the hydraulic cylinder 4 below the second draft control shaft 430 and to the left of the first draft control shaft 420, the hydraulic lifting device 100 can be made smaller as a whole. In this way, the degree of freedom in the layout of the components can be increased.

[0092] Therefore, the lift height of the lift arm 2 can be easily adjusted so that the traction load on the bracket 5 reaches the target magnitude, and the degree of freedom in the layout of the components can be increased. Furthermore, the hydraulic cylinder 4, which is one of the heaviest components, can be positioned lower in the internal space of the hydraulic lifting device 100. This allows the position of the center of gravity of the hydraulic lifting device 100 to be adjusted over a wide range.

[0093] For example, in this embodiment, the draft control lever 8 has one end 81 and another end 82 defined therein. The one end 81 is operable by an operator, and is rotatable relative to the case 1 with the other end 82 as a fulcrum, depending on the operation. The first draft control shaft 420 includes a same-direction rotation shaft 421, a reverse-direction rotation shaft 422, and a rotation transmission unit 423. The same-direction rotation shaft 421 is connected to the other end 82 of the draft control lever 8 and is rotatable in the same direction as the rotation of the draft control lever 8. The reverse-direction rotation shaft 422 is connected to the draft control cam 410 and is rotatable in the opposite direction to the rotation of the draft control lever 8. When the draft control lever 8 rotates relative to the case 1, the rotation transmission unit 423 transmits the rotation of the same-direction rotation shaft 421 to the reverse-direction rotation shaft 422 and rotates the reverse-direction rotation shaft 422 in the opposite direction to the rotation of the same-direction rotation shaft 421.

[0094] This allows the same-direction rotation shaft 421 and the opposite-direction rotation shaft 422 to be arranged with different axes via the rotation transmission unit 423. For example, as shown in FIG. 11, the position of the axis A1 of the same-direction rotation shaft 421 and the position of the axis A2 of the opposite-direction rotation shaft 422 can be made different from each other. This allows the same-direction rotation shaft 421 and the opposite-direction rotation shaft 422 to be laid out without interfering with the placement of the hydraulic cylinder 4, the control valve 5, and the like. In other words, this increases the degree of freedom in the layout of the first draft control shaft 420 and the draft control lever 8, allowing, for example, a layout that is easy for the operator to operate. Furthermore, by changing the link ratio in the rotation transmission unit 423, the displacement amount of the draft control cam 410 (the displacement amount of the spool 51) relative to the displacement amount of the draft control lever 8 can be adjusted. This allows the operating range of the draft control lever 8 to be adjusted to make it easier for the operator to operate it.

[0095] In particular, in this embodiment, either the first position control shaft 220 or the first draft control shaft 420 has a hollow structure, and is configured so that one can be coaxially fitted into the other. Either the second position control shaft 230 or the second draft control shaft 430 has a hollow structure, and is configured so that one can be coaxially fitted into the other.

[0096] More specifically, as shown in FIGS. 9, 11, and 12, the codirectional rotation shaft 221 of the first position control shaft 220 is coaxially fitted into the codirectional rotation shaft 421 of the first draft control shaft 420. The reverse direction rotation shaft 422 of the first draft control shaft 420 is coaxially fitted into the reverse direction rotation shaft 222 of the first position control shaft 220. The second position control shaft 230 is coaxially fitted into the second draft control shaft 430. In response to the displacement of either the position control lever 6 or the draft control lever 8, the first position control shaft 220 and the first draft control shaft 420 rotate relative to each other about axes A1 and A2. In response to the displacement of either the position feedback rod 9 or the draft feedback rod 10, the second position control shaft 230 and the second draft control shaft 430 rotate relative to each other about axis A3. This allows one shaft to be housed inside the other shaft, and space can be secured to accommodate the shafts, further increasing the degree of freedom in the layout of component parts.

[0097] <Modification> In the above embodiment, the co-directional rotation shaft 221 of the first position control shaft 220 is coaxially fitted into the co-directional rotation shaft 421 of the first draft control shaft 420. Alternatively, the co-directional rotation shaft 221 of the first position control shaft 220 may have a hollow structure, and the co-directional rotation shaft 421 of the first draft control shaft 420 may be coaxially fitted into the co-directional rotation shaft 221 of the first position control shaft 220.

[0098] In the above embodiment, the reverse rotation shaft 422 of the first draft control shaft 420 is coaxially fitted into the reverse rotation shaft 222 of the first position control shaft 220. Alternatively, the reverse rotation shaft 422 of the first draft control shaft 420 may have a hollow structure, and the reverse rotation shaft 222 of the first position control shaft 220 may be coaxially fitted into the reverse rotation shaft 422 of the first draft control shaft 420.

[0099] In the above embodiment, the second position control shaft 230 is coaxially fitted into the second draft control shaft 430. Alternatively, the second position control shaft 230 may have a hollow structure, and the second draft control shaft 430 may be coaxially fitted into the second position control shaft 230.

[0100] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0101] 1: Case 2: Lift arm 21: One end side 22:Other end side 3: Bracket 31: One end side 32:Other end side 4: Hydraulic cylinder 5: Control valve 51: Spool 6: Position control lever 61: One end side 62:Other end side 7: Pumpa Lever 71: One end side 72:Other end side 74: Rotation restriction part 8: Draft control lever 81: One end side 82:Other end side 9: Position feedback rod 91: Rear end side 92: Front end side 10: Draft feedback rod 101: Rear end side 102: Front end side 100: Hydraulic lifting device 20: Position control transmission mechanism 210: Position control cam 220: 1st position control shaft 221: Co-rotating shaft 222: Counter-rotating shaft 223: Rotation transmission part 230: Second position control shaft 30: Pump transmission mechanism 310: Pompakam 320: Pumpa shaft 330: Rotation transmission part 40: Draft control transmission mechanism 410: Draft control cam 420: 1st draft control shaft 421: Co-rotating shaft 422: Counter-rotating shaft 423: Rotation transmission part 430: 2nd position control shaft

Claims

1. Case and a hydraulic cylinder located inside the case and driven in response to the supply and discharge of hydraulic oil; a control valve located inside the case and having a spool in a flow path of the hydraulic oil, the control valve allowing and regulating the supply and discharge of the hydraulic oil to the hydraulic cylinder depending on the position of the spool; a lift arm located outside the case, having one end and the other end defined, the one end configured to be connectable to an object, and configured to rotate relative to the case with the other end as a fulcrum when the hydraulic cylinder is driven, thereby lifting and lowering the connected object; a position control lever located outside the case and configured to be displaceable in response to an operation by an operator; a position feedback rod located outside the case and configured to be displaceable in response to relative rotation of the lift arm; a position control transmission mechanism that, when the position control lever is operated, transmits the displacement of the position control lever toward the spool and displaces the position of the spool toward the side that allows supply and discharge of the hydraulic oil, and, when the lift arm rotates relatively, transmits the displacement of the position feedback rod toward the spool and displaces the position of the spool toward the side that restricts supply and discharge of the hydraulic oil; In a hydraulic lifting device comprising: The position control transmission mechanism includes: a first position control shaft that rotates about its axis in response to displacement of the position control lever when the position control lever is operated; a second position control shaft located above the first position control shaft in the lifting direction of the object, the second position control shaft rotating about its axis in response to displacement of the position feedback rod when the lift arm rotates relatively; a position control cam that, when the first position control shaft rotates, displaces the position of the spool toward a side allowing supply or discharge of the hydraulic oil in accordance with the rotation of the first position control shaft, and that, when the second position control shaft rotates, displaces the position of the spool toward a side restricting supply or discharge of the hydraulic oil in accordance with the rotation of the second position control shaft; A hydraulic lifting device equipped with

2. The hydraulic lifting device according to claim 1, The position control lever one end side and the other end side are defined, the one end side is configured to be operable by the operator, and is configured to be rotatable relative to the case with the other end side as a fulcrum as a displacement in response to the operation, The first position control shaft a co-rotation shaft connected to the other end of the position control lever and configured to be rotatable in the same direction as the rotation direction of the position control lever; a reverse rotation shaft connected to the position control cam and configured to be rotatable in a direction opposite to the rotation direction of the position control lever; a rotation transmission unit that transmits the rotation of the same-direction rotation shaft to the opposite-direction rotation shaft when the position control lever rotates relative to the same-direction rotation shaft, and rotates the opposite-direction rotation shaft in a direction opposite to the rotation direction of the same-direction rotation shaft; A hydraulic lifting device equipped with

3. The hydraulic lifting device according to claim 1 or 2, a pump lever located outside the case, the pump lever being displaceable from a first position, which is an arbitrary position when the supply and discharge of the hydraulic oil is regulated by the control valve, to a second position different from the first position in response to an operation by an operator; a pump transmission mechanism that, when the pump lever is operated to be displaced from the first position to the second position, transmits the displacement of the pump lever toward the spool and displaces the position of the spool toward the side that allows supply and discharge of the hydraulic oil, and that, when the lift arm rotates relatively with the pump lever located at the second position, transmits the displacement of the position feedback rod toward the spool and displaces the position of the spool toward the side that restricts supply and discharge of the hydraulic oil; Further provided with The pump transmission mechanism includes: a pump shaft that rotates about its axis in response to the displacement of the pump lever when the pump lever is operated and displaced from the first position to the second position; a pumper cam that, when the pumper shaft rotates, displaces the position of the spool toward a side that allows supply or discharge of the hydraulic oil in accordance with the rotation of the pumper shaft, and that, when the second position control shaft rotates, displaces the position of the spool toward a side that restricts supply or discharge of the hydraulic oil in accordance with the rotation of the second position control shaft; A hydraulic lifting device equipped with

4. The hydraulic lifting device according to claim 3, The pump lever is one end side and the other end side are defined, the one end side is configured to be operable by the operator, and is configured to be rotatable relative to the case with the other end side as a fulcrum as a displacement in response to the operation, a rotation restricting portion that restricts the relative rotation of the pump lever; A hydraulic lifting device equipped with

5. The hydraulic lifting device according to claim 1 or 2, a bracket located outside the case, having one end and the other end defined, the one end being configured to be connectable to an object, and the bracket rotating relative to the case with the other end as a fulcrum in response to a tractive load from the connected object; a draft control lever located outside the case and configured to be displaceable in response to an operation by an operator; a draft feedback rod located outside the case and configured to be displaceable in response to relative rotation of the bracket; a draft control transmission mechanism that, when the draft control lever is operated, transmits the displacement of the draft control lever toward the spool and displaces the position of the spool toward a side that allows supply and discharge of the hydraulic oil, and, when the bracket rotates relatively, transmits the displacement of the draft feedback rod toward the spool and displaces the position of the spool toward a side that restricts supply and discharge of the hydraulic oil; Further provided with The draft control transmission mechanism includes: a first draft control shaft that rotates about its axis in response to displacement of the draft control lever when the draft control lever is operated; a second draft control shaft that is located above the first draft control shaft in the lifting direction of the object and that rotates about its axis in response to displacement of the draft feedback rod when the bracket rotates relatively; a draft control cam that, when the first draft control shaft rotates, displaces the position of the spool toward a side that allows supply and discharge of the hydraulic oil in accordance with the rotation of the first draft control shaft, and that, when the second draft control shaft rotates, displaces the position of the spool toward a side that restricts supply and discharge of the hydraulic oil in accordance with the rotation of the second draft control shaft; A hydraulic lifting device equipped with

6. The hydraulic lifting device according to claim 5, one of the first position control shaft and the first draft control shaft has a hollow structure and is configured so that one can be coaxially fitted into the other, one of the second position control shaft and the second draft control shaft has a hollow structure and is configured so that one can be coaxially fitted into the other, The position control transmission mechanism and the draft control transmission mechanism are one of the first position control shaft and the first draft control shaft is coaxially fitted into the other, and one of the second position control shaft and the second draft control shaft is coaxially fitted into the other, In response to a displacement of either the position control lever or the draft control lever, the first position control shaft and the first draft control shaft rotate relatively to each other about their axes, The second position control shaft and the second draft control shaft are configured to rotate relatively to each other about their axes in response to displacement of either the position feedback rod or the draft feedback rod. Hydraulic lifting device.

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