Tractor

Abstract

To reduce a size of a vehicle body in a front-rear direction while having an operation link mechanism for transmitting change in a traction load to a lifting and lowering drive unit.SOLUTION: A tractor comprises: a lifting and lowering drive unit 9 for lifting- and lowering-driving a lift arm 25; a load detection member 21 which oscillates according to a traction load of a work device 12; and a mechanical linkage unit 22 which transmits an oscillation change of the load detection member 21 to the lifting and lowering drive unit 9. The lifting and lowering drive unit 9 comprises: an actuator; and a control unit which controls operation of the actuator. The mechanical linkage unit 22 includes an operation link mechanism 46 which operates the control unit by operating according to the oscillation change in the load detection member 21. The operation link mechanism 46 is provided in such a state that passes through a lateral side portion of the lift arm 25.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tractor equipped with a three-point linkage mechanism for attaching a work implement so that the implement can be raised and lowered. [Background technology]

[0002] The above-mentioned tractor is configured to perform plowing or other work with a work implement such as a plow attached to a three-point linkage mechanism, and is equipped with a mechanical linkage unit for draft control that converts changes in the tractive load acting on the work implement during work into a lift operation amount and transmits this to a hydraulic lift drive unit. Conventionally, the mechanical linkage unit has been equipped with an operation link mechanism configured by linking multiple links (see, for example, Patent Document 1).

[0003] In the device described in Patent Document 1, the operating link mechanism is provided in a state where it is displaced toward the front of the machine body relative to the lift arm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-42530 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described conventional configuration, the operating link mechanism is positioned toward the front of the vehicle body relative to the lift arm, which requires space to install the operating link mechanism in front of the lift arm, which has the disadvantage of increasing the size of the vehicle body in the fore-and-aft direction.

[0006] Therefore, there has been a demand for a vehicle that has an operating link mechanism for transmitting changes in traction load to the lift drive unit, while still being able to make the vehicle body more compact in the longitudinal direction. [Means for solving the problem]

[0007] A characteristic configuration of a tractor according to the present invention is that it comprises a three-point linkage mechanism connected to the rear of the vehicle body so as to be able to swing up and down and to which a working implement can be attached, a lift arm that can raise and lower the three-point linkage mechanism, a lift drive unit that drives the lift arm up and down, a load detection member that swings in accordance with the towing load of the working implement when the working implement is towed by the vehicle body and performing ground work, and a mechanical linkage unit that transmits changes in the swing of the load detection member to the lift drive unit, and the lift drive unit is equipped with an actuator and a control unit that controls the operation of the actuator, a protective frame is provided at the rear of the vehicle body, and left and right legs are provided on the protective frame so as to overlap the lift arms in a side view and to be positioned laterally outward of the lift arms; the mechanical linkage unit is provided with an operation link mechanism that operates in response to a swing change of the load detection member to operate the control unit, The operation link mechanism is provided in a state where it overlaps with the lift arm in a side view and is positioned between the lift arm and the leg. It's at the point.

[0008] According to the present invention, swing changes in the load detection member can be transmitted to the control unit via the mechanical linkage unit, and when the towing load is heavy, the working implement can be raised to reduce the load. Furthermore, because the operating link mechanism in the mechanical linkage unit is provided so as to pass through the lateral portion of the lift arm, the lift arm and the operating link mechanism are positioned so as to overlap in a side view. In other words, even if the operating link mechanism is long in the front-to-rear direction, the operating link can be positioned by effectively utilizing the free space on the lateral side of the lift arm, allowing for a compact arrangement in the front-to-rear direction as a whole.

[0009] Therefore, it is possible to make the vehicle body more compact in the longitudinal direction, even though it has an operating link mechanism that transmits changes in traction load to the lift drive unit.

[0010] In the present invention, it is preferable that a protective frame is provided at the rear of the vehicle body, the protective frame is provided with left and right legs positioned laterally of the lift arm, and the operating link mechanism is provided in a state where it passes between the lift arm and the legs.

[0011] According to this configuration, the operating link mechanism can be protected from the lateral outside by the legs, and damage to the operating link mechanism can be prevented.

[0012] In the present invention, it is preferable that the operating link mechanism is provided with an upright swing arm that swings in conjunction with changes in the swing of the load detection member, a forward / backward rod that is connected to the upright swing arm and is pushed and pulled in conjunction with the swing of the upright swing arm, and a downright swing arm that is connected to the downright portion of the rod and swings in conjunction with the pushing and pulling of the rod.

[0013] According to this configuration, by converting the swing change of the load detection member transmitted to the swing arm on the upstream side into a forward and backward movement of the rod facing forward and backward, the swing change can be reliably transmitted to the swing arm on the downstream side even if the rod is long in the forward and backward direction.

[0014] In the present invention, it is preferable to provide a screw-type distance adjustment unit that can change and adjust the distance between the connection point between the rod and the upstream swing arm and the connection point between the rod and the downstream swing arm.

[0015] According to this configuration, by changing the interval between the connection points by the interval adjuster, it is possible to change the response sensitivity in the operation of the hydraulic control valve in response to swing changes in the load detection member.

[0016] In the present invention, it is preferable that the device is provided with a horizontal support shaft extending horizontally, and a second swinging arm that swings integrally with the upstream swinging arm around the axis of the horizontal support shaft, the upstream swinging arm being configured to transmit the swing change transmitted to the second swinging arm to the rod, a support bracket that rotatably supports the horizontal support shaft, and a coil spring that is provided in a state where it is inserted onto the horizontal support shaft and that urges the upstream swinging arm to rotate toward the lowering operation side.

[0017] According to this configuration, a helical spring is provided as a biasing means for biasing the upper swing arm and the second swing arm toward the lowering operation side, effectively utilizing the horizontal support shaft provided to swingably support the upper swing arm and the second swing arm. A helical spring can be housed in a more compact shape than a coil spring, making it possible to reduce the size of the entire operation link mechanism.

[0018] In the present invention, a long hole is formed in the support bracket along the fore-and-aft direction of the vehicle body, the lateral support shaft is supported by the support bracket so that it can rotate and move in the fore-and-aft direction while being inserted through the long hole, a manually operable adjustment lever is provided on the front side of the lateral support shaft in the vehicle body, and a band-shaped operating member is provided which connects the adjustment lever to the lateral support shaft, and the adjustment lever is configured so that the position of the lateral support shaft can be changed in the fore-and-aft direction by operating the adjustment lever, thereby changing and adjusting the operating sensitivity of the mechanical linkage unit to swing changes of the load detection member, and the operating member is preferably bent so that a rear side portion of the operating member to which the lateral support shaft is connected is located outward in the lateral width direction of the vehicle body, and a front side portion of the operating member to which the adjustment lever is connected is located inward in the lateral width direction of the vehicle body.

[0019] According to this configuration, by changing the position of the horizontal support shaft forward or backward by operating the adjustment lever, the standby position of the downstream swing arm when the load detection member is in the standard position where it does not detect the traction load can be changed, and the operating sensitivity can be changed.

[0020] Furthermore, since the operating member that transmits the operation of the adjustment lever to the horizontal support shaft is formed in the shape of a strip, a complex connecting structure such as a universal joint is not required, as compared to when a rod is used, for example, and a simple connecting structure can be used.

[0021] In addition, the rear portion of the operating member supports the lateral support shaft from the outer side of the vehicle width, making it possible to protect the lateral support shaft from ridges, field soil, etc., and the front portion to which the adjustment lever is connected is located on the inner side of the vehicle width, making it possible to minimize protrusion in the vehicle width direction.

[0022] In the present invention, it is preferable that the coil spring is arranged in a position inward in the vehicle width direction of the rear portion of the operating member, and the adjustment lever is arranged in a position outward in the vehicle width direction of the front portion of the operating member.

[0023] According to this configuration, the coil spring and the adjustment lever are arranged rationally, effectively utilizing the free space created by the bent operating member, thereby making it possible to make the operating link mechanism more compact in the lateral width direction of the vehicle body.

[0024] In the present invention, it is preferable that a highly wear-resistant washer is provided at the sliding portion of the operating member and the support bracket.

[0025] The upper swing arm, the second swing arm, or the horizontal support shaft rotates frequently during operation. This can cause wear between the rotating members and the operating member, or between the rotating members and the support bracket. Therefore, with this configuration, highly wear-resistant washers are provided at the sliding points to prevent the above-mentioned wear. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. [Figure 2] FIG. 2 is a right side view of the main part showing the configuration of the lift drive unit and the mechanical linkage unit. [Figure 3] FIG. 2 is a plan view of the main parts showing the configuration of the lift drive unit and the mechanical linkage unit. [Figure 4] FIG. 2 is a rear view of the main part showing the configuration of the lift drive unit and the mechanical linkage unit. [Figure 5] FIG. 2 is a left side view of a main part showing the configuration of a lift drive unit and a mechanical linkage unit. [Figure 6] FIG. 2 is an exploded perspective view of a main part showing the configuration of a mechanical linkage unit. [Figure 7]FIG. 2 is an exploded perspective view of a main part showing the configuration of a mechanical linkage unit. [Figure 8] FIG. 2 is a cross-sectional plan view of a main part showing the configuration of a mechanical linkage unit. [Figure 9] FIG. 2 is an exploded perspective view showing a valve operating mechanism. [Figure 10] FIG. 2 is a linkage system diagram showing the linkage configuration of a mechanical linkage unit. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the direction indicated by the "F" arrow indicates the front side of the vehicle, the direction indicated by the "B" arrow indicates the rear side of the vehicle, the direction indicated by the "L" arrow indicates the left side of the vehicle, and the direction indicated by the "R" arrow indicates the right side of the vehicle. Therefore, the width direction of the vehicle corresponds to the left-right direction.

[0028] The tractor shown in Figure 1 is equipped with a pair of left and right front wheels 1, a pair of left and right rear wheels 2, a front frame 3, an intermediate frame 4, a clutch housing 5, a transmission case 6, a driver's section 7, and a pair of left and right rear fenders 8.

[0029] A pair of left and right front wheels 1 are journaled on a front frame 3 located at the front of the vehicle body and are located laterally outboard of the front frame 3. A clutch housing 5 is located between the front frame 3 and an intermediate frame 4. A transmission case 6 is connected to the rear end of the intermediate frame 4. The clutch housing 5 and transmission case 6 also serve as the body frame of the tractor. In other words, the front frame 3, intermediate frame 4, clutch housing 5, transmission case 6, etc. are connected together to form the body frame SF of the tractor. A rear support case 10 that supports a lifting drive unit 9 (described later) is provided above the transmission case 6.

[0030] An engine E is mounted and supported on the rear of the front frame 3, and a clutch housing 5 is connected to the lower rear end of the engine E. In addition, a pair of left and right rear wheels 2 are journaled on the transmission case 6, positioned on the left and right outer sides of the transmission case 6.

[0031] Although not shown in the figures, the clutch housing 5 houses a main clutch and other components, the intermediate frame 4 is provided with a transmission shaft, and the transmission case 6 houses a main transmission, an auxiliary transmission, and other components. Power from the engine E is transmitted to a pair of left and right front wheels 1 and a pair of left and right rear wheels 2 via the main clutch, transmission shaft, main transmission, auxiliary transmission, and other components. A PTO shaft 13 is provided that protrudes rearward from the rear of the transmission case 6 and is capable of outputting power to be transmitted to a working device 12.

[0032] The driver's section 7 is located at the rear of the vehicle body and is configured to allow an operator to ride in it. The driver's section 7 is equipped with a steering wheel 14 and a driver's seat 15. Rear fenders 8 are located on the left and right sides of the driver's seat 15 on the outer side of the vehicle body, and the rear fenders 8 cover the left and right rear wheels 2 from above. The transmission case 6 is located below the driver's seat 11.

[0033] A front protective frame 16 is provided at the front-rear intermediate portion of the vehicle body, rising from both the left and right sides of the intermediate frame 4 and extending in a detouring upward direction. Also, a rear protective frame 17 is provided at the rear of the vehicle body, positioned behind the driver's seat 15, rising from the left and right lateral portions of the transmission case 6 and extending in a detouring upward direction. The rear protective frame 17 has left and right legs 18 formed upright from the transmission case 6 and an upper arch portion 19, and is provided lower than the front protective frame 16.

[0034] A three-point linkage 20 is connected to the rear of the transmission case 6 so that it can swing up and down. The three-point linkage 20 has left and right lower links 20a and left and right central top links 20b, and supports a working implement 12 so that it can be raised and lowered. The working implement 12 shown in Figure 1 is a plow. As the working implement 12, for example, a tow-type working implement 12 such as a disc harrow, cultivator, subsoiler, rotary, etc. can be attached, but is not limited to these.

[0035] Left and right lift arms 25 are provided to suspend and support the left and right lower links 20 a of the three-point link mechanism 20 via the left and right lift rods 23 .

[0036] The machine is equipped with a hydraulic lifting drive unit 9 that drives the three-point link mechanism 20 to raise and lower while the working implement 12 is connected, a load detection member 21 that swings in accordance with the towing load of the working implement 12 when the working implement 12 is towed by the vehicle body and performing ground work, and a mechanical linkage unit 22 that transmits swing changes of the load detection member 21 to the lifting drive unit 9.

[0037] [Drive lift unit] The lifting drive unit 9 includes a hydraulic cylinder 26 as an actuator that drives the left and right lift arms 25 to swing up and down, a hydraulic control valve 27 as a control unit that controls the supply and discharge of hydraulic oil to the hydraulic cylinder 26, a height setting lever 28 that sets the control target height of the working device 12, a valve operating mechanism 29 that links a spool 27A of the hydraulic control valve 27 by operating the height setting lever 28 and the mechanical linkage unit 22, and a feedback link mechanism 30 that links the spool 27A to the left and right lift arms 25. The hydraulic control valve 27 includes an internal biasing means (not shown) that biases the spool 27A back to a lowered position toward the front of the vehicle body. The height setting lever 28 is supported by the rear support case 10 so as to be swingable back and forth about the axis of a horizontal lever support shaft 31, and extends above the rear fender 8 to the right of the driver's seat 15.

[0038] As shown in Figures 9 and 10, the valve operating mechanism 29 includes an operating arm 32 that can be swung by operating the height setting lever 28 and the mechanical linkage unit 22, a balance arm 33 that is supported on the spool 27A of the hydraulic control valve 27 so as to be able to swing back and forth around the vertical axis, and an operating member 34 that is swung in conjunction with the swing of the operating arm 32 and is movably engaged with one end of the balance arm 33.

[0039] The valve operating mechanism 29 moves the spool 27A of the hydraulic control valve 27 from the neutral position to the raised position or lowered position in conjunction with the swing operation of the height setting lever 28. The valve operating mechanism 29 also moves the spool 27A in response to the operation of the mechanical linkage unit 22.

[0040] The feedback link mechanism 30 includes a connecting link 35 extending from the left lift arm 25 toward the front of the vehicle body, and an operating member 36 that engages with the other end of the balance arm 33 via the connecting link 35. When the working implement 12 reaches the target height, the feedback link mechanism 30 moves the spool 27A of the hydraulic control valve 27 from the raised or lowered position to the neutral position in response to the reaching of the target height.

[0041] The operating arm 32 has a slot 32a formed in the swing direction. An interlocking portion 28a extends downward and forward from the height setting lever 28, and a pin 28b that fits into the slot 32a is provided in the interlocking portion 28a. When the height setting lever 28 is operated to the height-increasing side (rearward), the operating arm 32 swings rearward via the pin 28b, and the spool 27A is operated to the raised position. When the hydraulic cylinder 26 operates to raise the lift arm 25 to a position corresponding to the set height of the height setting lever 28, the feedback link mechanism 30 is operated to return the spool 27A to its neutral position, and the lift arm 25 is maintained at the set height suitable for tilling work.

[0042] When the operating arm 32 is pulled rearward due to an increase in the traction load by operating the mechanical linkage unit 22 described below, the long hole 32a allows it to swing rearward, allowing the lift arm 25 to be raised.

[0043] [Load detection member] 5 and 6, the load detection member 21 is supported by a rear frame 37 fixed to the rear end of the rear support case 10 so as to be swingably displaceable in the front-to-rear direction via a horizontal support shaft 38 at the bottom. The load detection member 21 is biased to swing toward the rear of the vehicle body by a coil spring 39 provided on the front side. In addition, the range of swinging of the load detection member 21 for the front and rear is limited by a limiting mechanism consisting of an elongated hole 40 formed in the rear frame 37 and a pin 41 provided on the load detection member 21.

[0044] As shown in Fig. 5, the front end of the top link 20b of the three-point linkage 20 is connected to the load detection member 21 via a connecting pin 42. Also, as shown in Fig. 1, the front ends of the left and right lower links 20a are connected to left and right brackets 43 provided at the rear end of the transmission case 6 via left and right connecting pins 44. With this connection structure, the traction load during plowing acts on the load detection member 21 via the top link 20b.

[0045] When the traction load becomes large, the load detection member 21 swings from the standard position (standby state) toward the front of the vehicle body against the biasing force of the coil spring 39 in conjunction with the increase in the traction load, and swings toward the rear of the vehicle body due to the biasing force of the coil spring 39 in conjunction with the decrease in the traction load, returning to the standard position.

[0046] [Mechanical linkage unit] The mechanical linkage unit 22 is configured to transmit the swing displacement caused by the traction load of the load detection member 21 to the operating arm 32 of the valve operating mechanism 29. As shown in Fig. 4, the mechanical linkage unit 22 is provided with: a first linkage mechanism 45 provided on the left side, which is one side in the left-right direction of the body frame SF, and interlocked with the load detection member 21; a second linkage mechanism 46 provided on the right side, which is the other side in the left-right direction of the body frame SF, as an operating linkage mechanism interlocked with the lift drive unit 9; and an operating cable 47 interlocking and interlocking the first linkage mechanism 45 and the second linkage mechanism 46.

[0047] The first link mechanism 45 will now be described. As shown in Figures 5, 6 and 10, the first link mechanism 45 is provided with an interlocking member 48 that is provided on the left side of the upper part of the load detection member 21 and that swings in conjunction with the load detection member 21, and a swing operating member 50 that is supported so as to be swingable around the horizontal axis by a bracket 49 that serves as a support member fixed to the rear frame 37.

[0048] The interlocking member 48 is formed in the shape of a strip that is long in the vertical direction, and its vertical middle portion is supported by the load detecting member 21 so as to be swingable around the axis of the horizontal support shaft 48A. A receiving member 51 is provided on the load detecting member 21 at a location on the rear side of the swing fulcrum portion of the interlocking member 48, and when the load detecting member 21 swings forward, it is received by the receiving member 51 and the interlocking member 48 swings forward in conjunction with it.

[0049] The swing operation member 50 has an upper arm portion 52 and a lower arm portion 53, and is formed from a plate body formed into a substantially L-shape in side view. The swing operation member 50 is swingably supported at its middle portion by a bracket 49 via a horizontal support shaft 55. The bracket 49 is connected and fixed to the rear frame 37. A contact roller 56 supported on the lower end of the interlocking member 48 is configured to be able to come into contact with the upper arm portion 52 as the interlocking member 48 swings forward, and the swing end of the lower arm portion 53 is connected to the end of the operation cable 47 on the load detection member 21 side.

[0050] The swing operation member 50 is biased by a coil spring 57 attached to a support shaft 55 to rotate the upper arm portion 52 in a direction approaching the interlocking member 48. Therefore, in the initial state where no traction load is applied, the upper arm portion 52 is in contact with the interlocking member 48.

[0051] When the load detection member 21 swings forward from the standby position due to a traction load, the interlocking member 48 and the upper arm 52 swing forward in unison, and the lower arm 53 swings upward, pulling the operation cable 47 upward. When the traction load is removed, the initial state is restored. The lower arm 53 is configured to swing up and down around a horizontal position in response to operation of the operation cable 47, which extends in the vertical direction.

[0052] The first link mechanism 45 is provided with a change amount adjustment mechanism 58 that can change the amount of relative displacement of the interlocking member 48 with respect to the pivotal displacement of the load detection member 21 in two stages. As shown in FIGS. 3 to 6, the change amount adjustment mechanism 58 includes a base member 59 that is supported on the rear frame 37 so as to be rotatable about the longitudinal axis X, a grip operation unit 60 that operates to pivot the base member 59, and an operation restriction unit 61 that is supported on the base member 59. The operation restriction unit 61 is switchable between a state in which it is located within the movement range of the interlocking member 48 as the base member 59 pivots (the state shown in FIGS. 4 and 5) and a state in which it is located outside the movement range.

[0053] 4 and 5 about the longitudinal axis X in the counterclockwise direction in FIG. 4, when the operation regulating unit 61 is moved out of the range of movement, the interlocking member 48 swings integrally with the load detecting member 21. When the operation regulating unit 61 is located within the range of movement, a portion of the interlocking member 48 above the support shaft 48A comes into contact with the operation regulating unit 61 midway through the swing, increasing the amount of operation of the interlocking member 48. This makes it possible to change the amount of operation transmitted to the operating arm 32 in response to the amount of displacement of the load detecting member 21, for example, depending on differences in the hardness of the soil in the field.

[0054] The second link mechanism 46 will now be described. 2 to 4, 7, and 10, second link mechanism 46 is provided with: a linking member 62 that is generally L-shaped in side view and has one end connected to operation cable 47; a push / pull rod 63 extending forward and backward as a linking member that is connected to the other end of linking member 62 and is pushed or pulled in response to the swing of linking member 62 to transmit the amount of operation; and an operating arm 64 that is connected to the rear end of push / pull rod 63 and serves as a downstream swing arm that swings in conjunction with the pushing and pulling. Actuating arm 64 is rotatably supported by operating arm 32 of valve operating mechanism 29.

[0055] 4, a second link mechanism 46 is provided so as to pass through a lateral portion of the lift arm 25. The second link mechanism 46 is provided so as to pass between the right lift arm 25 and the right leg 18 of the rear protective frame 17.

[0056] The linking member 62 is integrally formed into a substantially L-shape and includes a first relay arm 65 to which the downstream end of the operation cable 47 is connected, and a second relay arm 66 that swings integrally with the first relay arm 65. The linking member 62 has an intermediate portion supported by a support bracket 68 so as to be swingable around the axis of a horizontal support shaft 67 that extends laterally.

[0057] The operating cable 47 is connected to the swinging end of the first relay arm 65, and the front end of the push / pull rod 63 is connected to the swinging end of the second relay arm 66. When the linking member 62 swings via the operating cable 47 in response to the swing of the load detection member 21, the push / pull rod 63 is operated, and the operating arm 64 swings by an operating amount corresponding to the swing amount of the load detection member 21. As the operating arm 64 swings, the operating arm 32 swings.

[0058] 2 and 7, there is provided a screw-type distance adjustment unit 69 that can change and adjust the distance between the connection point between the push / pull rod 63 and the second relay arm 66 and the connection point between the push / pull rod 63 and the operating arm 64. Specifically, a threaded portion is formed in the front portion of the push / pull rod 63, and this threaded portion is provided in a state where a cylindrical connector 70 that is supported on the second relay arm 66 so as to be rotatable about a horizontal axis is inserted through this threaded portion.

[0059] Nuts 71 are attached to both the front and rear of the connector 70 on the threaded portion of the push / pull rod 63. By loosening the front and rear nuts 71 and moving the push / pull rod 63 forward or backward, the distance between the connection point between the push / pull rod 63 and the second relay arm 66 and the connection point between the push / pull rod 63 and the operating arm 64 can be changed, and the position can be fixed by tightening the nuts 71 on both sides. The rear end of the push / pull rod 63 is bent approximately 90 degrees in a plan view and pivotally connected to the operating arm 64 so as to be rotatable.

[0060] 2 and 7, a sensitivity adjustment mechanism 72 is provided that adjusts the actuation sensitivity when the spool 27A is interlocked with the load detection member 21. The sensitivity adjustment mechanism 72 includes a sensitivity adjustment lever 73 provided on the right side of the driver's seat 15, an operation member 74 extending from the sensitivity adjustment lever 73 to the lateral support shaft 67 of the linking member 62, and a vehicle-side support bracket 75 that supports the lateral support shaft 67 so that its position can be changed. The sensitivity adjustment lever 73 is supported on the rear support case 10 so as to be swingable back and forth about a lever support shaft 31 that is also shared with the height setting lever 28, and extends above the rear fender 8 to the right of the driver's seat 15. The lever support shaft 31 is provided with a friction retaining portion that retains the sensitivity adjustment lever 73 in any operating position.

[0061] 3 and 8, the support bracket 75 is fixed to the side wall of the rear support case 10 and is bent outward in a generally L-shape in plan view. A long hole 76 that is long in the front-to-rear direction is formed in the outermost vertical surface portion 75a of the support bracket 75. A horizontal support shaft 67 is inserted through this long hole 76 and is provided so as to be movable in the front-to-rear direction along the long hole 76.

[0062] As the sensitivity adjustment lever 73 is swung, the operating member 74 is pushed and pulled, changing the position of the horizontal support shaft 67 back and forth along the elongated hole 76. In conjunction with this, the gap between the operating arm 64 and the connecting portion 32b of the operating arm 32 changes, making it possible to adjust the operating sensitivity when the spool 27A of the hydraulic control valve 27 is connected to the load detection member 21.

[0063] As shown in FIG. 7, the linking portion 32b of the operating arm 32 is provided in a substantially U-shape in plan view, and the operating arm 64 is rotatably supported by a support shaft 64a while positioned inside the linking portion 32b. Operating the sensitivity adjustment lever 73 changes the relative position (reference position) between the operating arm 64 and the operating arm 32 when no traction load is applied. When the operating arm 64 swings from the reference position in conjunction with the load detection member 21, the operating arm 32 can be switched between a state in which it operates sensitively and a state in which it has low responsiveness and low sensitivity in accordance with the change in the reference position.

[0064] 8, a coil spring 77 is provided which rotationally biases the linking member 62 toward the lowering operation side while being fitted onto the horizontal support shaft 67. The coil spring 77 is provided on the inner left-right side of the vertical surface portion 75a of the support bracket 75. The coil spring 77 is configured to rotationally bias the spool 27A of the hydraulic control valve 27 toward the lowered position, i.e., to rotate the first relay arm 65 upward.

[0065] 3 and 7, the operating member 74 is formed in the shape of a strip and is bent midway so that its front side is located on the inner side in the left-right direction and its rear side is located on the inner side in the left-right direction. The front side, to which the sensitivity adjustment lever 73 is connected, is located on the inner side in the left-right direction and is oriented along the front-to-back direction, while the rear side, to which the lateral support shaft 67 is connected, is located on the outer side in the left-to-right direction and is oriented along the front-to-back direction. The intermediate portion between the front side and the rear side is oriented inward in the left-to-right direction as it approaches the front.

[0066] The operating member 74 is positioned on the outer side in the left-right direction of the vertical surface portion 75a of the support bracket 75, supported by the horizontal support shaft 67, and held in position by fastening a nut 78 (see FIG. 8).

[0067] The coil spring 77 is provided so as to be located on the left-right inward side of the rear portion of the operating member 74. The sensitivity adjustment lever 73 is provided so that its base end portion is located on the left-right inward side of the front portion of the operating member 74, but its upper portion is located on the left-right outward side. Therefore, it is provided so as to be located on the left-right outward side of the front portion of the operating member 74.

[0068] The horizontal support shaft 67 is configured to rotate integrally with the linking member 62. Highly wear-resistant washers 79 are provided at the sliding points between the operating member 74 and the rotating parts of the support bracket 75 to prevent wear.

[0069] The sensitivity adjustment lever 73 and the height setting lever 28 are positioned so that their upper portions are close to each other in the left-right direction to facilitate operation from the driver unit 7. The base end portions of the sensitivity adjustment lever 73 and the height setting lever 28 are spaced apart along the axial direction (left-right direction) of the lever support shaft 31. A push-pull rod 63 is provided so as to pass through this spaced apart portion. The push-pull rod 63 is bent at its front-to-rear midpoint so as to pass between the base end portions of the sensitivity adjustment lever 73 and the height setting lever 28. In this way, the second link mechanism 46 rationally arranges each member to make the left-to-right width as compact as possible.

[0070] [Operation cable] 2, 4, 6, and 10, the operation cable 47 includes an inner cable 47A and an outer cable 47B that slidably supports the inner cable 47A by externally fitting it therearound. The upstream end of the operation cable 47 on the load detection member 21 side (hereinafter simply referred to as the upstream end), specifically the upstream end of the inner cable 47A, is connected to the lower arm portion 53 of the swing operation member 50 in the first link mechanism 45. The downstream end of the operation cable 47 on the lift drive unit 9 side (hereinafter simply referred to as the downstream end), i.e., the downstream end of the inner cable 47A, is connected to the first relay arm 65 of the linkage member 62 in the second link mechanism 46.

[0071] As described above, the lower arm portion 53 of the swing operation member 50 to which the operation cable 47 is connected and the first relay arm 65 of the linking member 62 are configured to swing up and down around a horizontal position, and even if the inner wire 46A slides in conjunction with the swing of the lower arm portion 53 or the first relay arm 65, it is possible to prevent the inner wire 46A from sliding strongly against the end of the outer cable 47B and becoming worn.

[0072] 4, the upstream end of outer cable 47B is supported by an outer cable support member 81 fixed to bracket 49. Bracket 49 is fixedly supported by rear frame 37. The downstream end of outer cable 47B is supported by an outer cable support member 82 serving as a bracket fixedly extended from transmission case 6.

[0073] The connection portion between the downstream end of the inner cable 47A and the first relay arm 65 is located closer to the front of the vehicle body than the connection portion between the upstream end of the inner cable 47A and the lower arm portion 53.

[0074] The upstream end of the operation cable 47 is provided so as to extend in the vertical direction. That is, the upstream end of the inner cable 47A and the outer receiving member 81 are provided at positions spaced apart in the vertical direction while substantially overlapping in a plan view. The downstream end of the operation cable 47 is provided so as to extend in the vertical direction. That is, the downstream end of the inner cable 47A and the outer receiving member 82 are provided at positions spaced apart in the vertical direction while substantially overlapping in a plan view.

[0075] 2, 4, and 5, the operation cable 47 is provided such that the upstream end of the operation cable 47 on the load detection member 21 side and the downstream end of the operation cable 47 on the lift drive unit 9 side each extend in the up-down direction. Also, as shown in FIGS. 1 and 3, the operation cable 47 is provided such that the downstream end is located further forward than the upstream end. The downstream end of the operation cable 47 is provided such that it is located further forward of the rear wall 6A of the transmission case 6.

[0076] As shown in FIG. 4, the operating cable 47 extends downward from a position higher than the PTO shaft 13, passes below the PTO shaft 13, and extends to a position higher than the PTO shaft 13.

[0077] That is, the operating cable 47 is arranged so that the upstream end and downstream end are connected and supported by outer support members 81, 82 at locations above the PTO shaft 13, and the middle portion passes through the area below the PTO shaft 13.

[0078] The operation cable 47 is routed along the rear wall 6A of the transmission case 6. A locking member 83 is provided in a location on the rear wall 6A corresponding to the area below the PTO shaft 13, and an intermediate portion of the operation cable 47 is locked and held by the locking member 83. Therefore, the operation cable 47 curves with a large radius of curvature from the first link mechanism 45 toward the second link mechanism 46, passing through an area below the PTO shaft 13.

[0079] The locking member 83 is elongated and has a length in the left-right direction that is approximately the same as the left-right width of the rear wall 6A of the transmission case 6. By locking the lower intermediate portion of the operation cable 47 over a wide range in the left-right direction in this manner, the operation cable 47 can be maintained in a stable position.

[0080] [Another embodiment] Other embodiments will be listed below.

[0081] (1) Instead of the linking member 62 in which the second relay arm 66 (upper-side swing arm) and the first relay arm 65 (second swing arm) are integrally formed in an approximately L-shape, the push-pull rod may be operated by a swing arm on the upper side, a support shaft that rotates integrally with the swing arm, and a second swing arm that is separate from the swing arm on the upper side.

[0082]

[0083] ( 2 Instead of the rod 63 extending in the forward and backward directions, a push-pull operation cable may be used for interlocking.

[0084] ( 3 ) The screw-type distance adjustment part 69 may be provided at the connection point between the push / pull rod 63 and the operating arm 64. Also, instead of being provided at the connection point between the push / pull rod 63 and the second relay arm 66 and the connection point between the push / pull rod 63 and the operating arm 64, a turnbuckle mechanism may be provided midway along the push / pull rod 63 to change the length of the rod itself.

[0085] ( 4 The mechanical linking unit 22 may not include the operation cable 47 and may be configured entirely from link members.

[0086] ( 5 ) The mechanical linking units 22 may be arranged together on one side of the body frame SF in the left-right direction or on the other side of the body frame SF in the left-right direction, rather than being distributed between the left and right.

[0087] ( 6 The operating member 74 may have a rear portion located on the inner side in the left-right direction and a front portion located on the outer side in the left-right direction, or the front and rear portions may be located at approximately the same position in the left-right direction. The operating member 74 may also be formed of a rod.

[0088] ( 7 ) A configuration in which the highly wear-resistant washer 79 is not provided is also possible.

[0089] ( 8 The load detection member 21 may be supported so as to be swingable around a horizontal support shaft at the top, or may be supported so as to be swingable around a vertical shaft.

[0090] ( 9 As the actuator for driving the three-point link mechanism 20 to move up and down, an electric actuator such as an electric cylinder or an electric motor may be used instead of a hydraulic cylinder.

[0091] ( 10 The tractor configuration can be modified in various ways. For example, it may be configured with crawler travel devices instead of the left and right rear wheels, or it may be configured with crawler travel devices instead of the left and right front wheels and the left and right rear wheels. It may be an electric configuration with an electric motor instead of an engine, or a hybrid configuration with an engine and an electric motor. [Industrial Applicability]

[0092] The present invention is applicable to a tractor equipped with a three-point linkage mechanism that mounts a work implement so that it can be raised and lowered. [Explanation of symbols]

[0093] 9 Lifting drive unit 12 Work equipment 17 Protective Frame 18 Legs 20 Three-point linkage mechanism 21 Load detection member 25 lift arm 26 Hydraulic cylinder (actuator) 27 Hydraulic control valve (control unit) 46 Operation link mechanism 63 Rod 64 Downstream swing arm 65 Second swing arm 66 Right side swing arm 67 Horizontal support shaft 68 Support bracket 73 Adjustment lever 74 Operating member 76 long hole 77 Coil spring 79 Washer

Claims

1. a three-point link mechanism connected to the rear of the vehicle body so as to be able to swing up and down and to which a working device can be attached; a lift arm capable of lifting and lowering the three-point link mechanism; an elevation drive unit that drives the lift arm to elevate; a load detection member that swings in response to a towing load of the working device when the working device is towed by the vehicle body and performing ground work; a mechanical linking unit that transmits a swing change of the load detecting member to the lifting drive unit, The lifting drive unit is provided with an actuator and a control unit that controls the operation of the actuator, A protective frame is provided at the rear of the vehicle body, The protective frame is provided with left and right legs that overlap the lift arms in a side view and are positioned laterally outward of the lift arms, the mechanical linkage unit is provided with an operation link mechanism that operates in response to a swing change of the load detection member to operate the control unit, The tractor is provided with the operation link mechanism so as to overlap with the lift arm in a side view and so as to be positioned between the lift arm and the leg.

2. The tractor of claim 1, wherein the operating link mechanism is provided with an upstream swing arm that swings in conjunction with changes in the swing of the load detection member, a forward / backward rod that is connected to the upstream swing arm and is pushed and pulled in conjunction with the swing of the upstream swing arm, and a downstream swing arm that is connected to a downstream portion of the rod and swings in conjunction with the pushing and pulling of the rod.

3. 3. A tractor according to claim 2, further comprising a screw-type distance adjustment unit that can change and adjust the distance between the connection point between the rod and the upstream swing arm and the connection point between the rod and the downstream swing arm.

4. a horizontal support shaft extending in the horizontal direction; a second swing arm that swings integrally with the upstream swing arm around the axis of the horizontal support shaft, The upstream swing arm is configured to transmit the swing change transmitted to the second swing arm to the rod, 4. A tractor as described in claim 2 or 3, further comprising: a support bracket that rotatably supports the horizontal support shaft; and a coil spring that is fitted onto the horizontal support shaft and urges the upper swing arm to rotate toward the lowering operation side.

5. The support bracket is formed with a long hole extending along the front-rear direction of the vehicle body, the horizontal support shaft is supported by the support bracket so as to be rotatable and movable in the front-rear direction while being inserted through the long hole, a manually operable adjustment lever provided on the vehicle body front side of the lateral support shaft; a band-shaped operating member that connects the adjustment lever and the horizontal support shaft, By operating the adjustment lever, the position of the lateral support shaft can be changed in the front-rear direction, thereby changing and adjusting the operation sensitivity of the mechanical linkage unit to a swing change of the load detection member, The tractor according to claim 4, wherein the operating member is bent so that the rear portion of the operating member to which the lateral support shaft is connected is located on the outer side in the vehicle width direction, and the front portion of the operating member to which the adjustment lever is connected is located on the inner side in the vehicle width direction.

6. the coil spring is provided in a state where it is located on the inner side of the rear portion of the operating member in the vehicle body width direction, 6. The tractor according to claim 5, wherein the adjustment lever is provided in a state where it is located outward in the vehicle body width direction at the front side portion of the operating member.

7. 7. A tractor according to claim 5, wherein highly wear-resistant washers are provided at sliding points between the operating member and the support bracket.

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