JP2017195824A - Tractor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tractor that enables draft control with high control accuracy while being made advantageous in terms of productivity.SOLUTION: A tractor includes: a lift arm 15 for suspending and supporting a towed working device; a hydraulic actuator 16 for vertically swinging and driving the lift arm 15; a control valve 17 for controlling the operation of the hydraulic actuator 16; a load detection member 21 supported to a supporting member 37 fixed at the rear of a vehicle body in a displacing manner; a biasing mechanism 60 for displacing and biasing the load detection member 21 in the direction against a towing load applied on the load detection member 21; and a link mechanism 22 for interlocking a spool 17A of the control valve 17 to the load detection member 21. The biasing mechanism 60 includes a coil spring 61 for permitting displacement of the load detection member 21 according to the towing load when the towing load exceeds a set value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a tractor including a mechanical draft control system that raises and lowers a towed working device according to a tow load.

  In the tractor as described above, there is a tractor in which a top link hitch that receives a traction load is connected to a bracket fixed to a rear end portion of a transmission case via a torsion bar (see, for example, Patent Document 1).

JP 2011-30431 A (paragraph number 0024, FIG. 1, FIG. 3, FIG. 4)

In the configuration described in Patent Document 1, the left end portion of the torsion bar is pin-connected to the left boss portion of the bracket. The right end side of the torsion bar is pin-connected to the right end portion of the boss portion in the top link hitch. The right end portion of the torsion bar is rotatably supported by the right boss portion of the bracket. When the traction load acts on the top link hitch, the traction load acts on the torsion bar via the top link hitch as a torsional force. When this torsional force becomes greater than the restoring force of the torsion bar, the top link hitch is moved to the reference position. The traction load decreases as the working device rises in conjunction with the oscillating displacement.
After that, when the traction load decreases and the torsional force acting on the torsion bar becomes smaller than the restoring force of the torsion bar, the top link hitch swings and displaces toward the reference position by the restoring force of the torsion bar. The traction load increases as the work device descends in conjunction with the displacement.

In other words, in order to properly raise and lower the work device according to the traction load, it is necessary to accurately support the left and right ends of the torsion bar with the left and right bosses of the bracket without any misalignment. If it occurs, the traction load acts on the torsion bar in a state where the torsional force and the bending force are distributed.
As a result, in order to raise and lower the working device appropriately according to the traction load, it is necessary to assemble the torsion bar in a state where the accuracy of supporting the torsion bar by the bracket is increased, and there is room for improvement in terms of productivity. There is.

  That is, it is desired to enable draft control with high control accuracy while being advantageous in terms of productivity.

As means for solving the above problems,
A tractor according to the present invention includes a lift arm that suspends and supports a tow-type working device, a hydraulic actuator that swings and drives the lift arm in a vertical direction, a control valve that controls the operation of the hydraulic actuator, and a rear part of a vehicle body A load detection member that is displaceably supported by a support member fixed to the load member, a biasing mechanism that biases the load detection member in a direction against a traction load applied to the load detection member, and a spool of the control valve A link mechanism for interlocking with the load detection member,
The urging mechanism includes a coil spring that allows displacement of the load detection member according to the traction load when the traction load exceeds a set value.

According to this means, when one end portion of the coil spring is connected to the support member and the other end portion of the coil spring is connected to the load detection member, when the traction load acting on the load detection member exceeds the set value, The detection member is displaced according to the traction load, and the spool of the control valve is displaced in conjunction with the displacement. The displacement of the spool at this time makes it possible to raise the work device and reduce the traction load. When the traction load decreases and becomes smaller than the elastic force of the coil spring, the load detecting member is displaced by the elastic force of the coil spring, and the spool of the control valve is displaced in conjunction with this displacement. It is possible to raise the traction load by lowering the working device.
That is, the work device can be raised and lowered appropriately according to the traction load by simple assembly in which the coil spring is connected to the support member and the load detection member.
As a result, it is possible to enable draft control with high control accuracy while being advantageous in terms of productivity.

As one of the means for making the present invention more suitable,
The load detection member is supported by the support member so as to be able to swing and displace via a support shaft,
The urging mechanism is disposed between the support member and the free end portion of the load detection member.

  According to this means, for example, the position of the urging mechanism is separated from the oscillating fulcrum of the load detecting member as compared with the case where the urging mechanism is provided between the supporting member and the oscillating fulcrum side of the load detecting member. Thus, as a coil spring provided in the urging mechanism without changing the set value described above, it is possible to employ a light and easy-to-handle inexpensive weak spring with a small spring constant.

As one of the means for making the present invention more suitable,
A regulation mechanism for regulating displacement of the load detection member;
The restriction mechanism is disposed at a position between the support shaft and the urging mechanism between the support member and the load detection member.

  According to this means, the regulating mechanism is equipped using the space between the support shaft and the biasing mechanism formed by arranging the biasing mechanism between the support member and the free end portion of the load detection member. Therefore, unnecessary displacement of the load detection member can be prevented while preventing an increase in size caused by disposing the restriction mechanism at a position deviated from between the support shaft and the biasing mechanism.

As one of the means for making the present invention more suitable,
The regulation mechanism is inserted into the elongated hole formed in one of the support member and the load detection member so as to be long in the displacement direction of the load detection member, and the other of the support member and the load detection member. With a pin that is equipped in a mounted state.

  According to this means, an unnecessary displacement of the load detection member can be reliably prevented with a simple configuration in which one of the support member and the load detection member is provided with a long hole and the other is provided with a pin.

As one of the means for making the present invention more suitable,
The urging mechanism includes a spring force adjusting unit that enables the setting value to be changed.

According to this means, the operator can change the set value described above according to the hardness of the soil of the work place that affects the traction load.
Thereby, draft control suitable for a work place can be performed.

It is a right view of the tractor provided with the working device. It is a vertical right view of the principal part which shows the structure of a mechanical linkage type hydraulic lifting apparatus. It is a disassembled perspective view of the principal part which shows the structure of a mechanical linkage type hydraulic lifting apparatus. It is a vertical right side view of the principal part showing the operating state of the hydraulic lifting device when the working device is stopped by holding the position of the height setting lever on the lower position side. It is a vertical right side view of the principal part showing the operating state of the hydraulic lifting device when the working device is lifted in conjunction with the swinging operation of the height setting lever in the high setting direction. It is a vertical right side view of the principal part showing the operating state of the hydraulic lifting device when the working device is lifted and stopped by holding the position of the height setting lever on the high position side. It is a vertical rear view of the principal part which shows the structure of a mechanical linkage type hydraulic lifting apparatus. It is a cross-sectional top view of the principal part which shows the structure of a mechanical linkage type hydraulic lifting apparatus. FIG. 5 is a longitudinal right side view of a main part showing a state in which an operation arm swings in a high setting direction and presses a first swing arm in conjunction with the swing of the load detection member toward the front of the vehicle body. Longitudinal section of the main part showing the state where the sensitivity adjustment mechanism is changing the fixed position of the swing fulcrum shaft of the relay arm in conjunction with the operation of the sensitivity adjustment lever to change the gap between the first swing arm and the operation arm It is a right view. It is a vertical right view of the principal part which shows structures, such as a biasing mechanism and a control mechanism. It is a cross-sectional top view of the principal part which shows the support structure of the cover member for accelerator levers.

  Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the drawings.

  The direction indicated by the arrow F shown in FIG. 1 is the front side of the tractor, and the direction indicated by the arrow U is the upper side of the tractor.

  As shown in FIG. 1, the tractor exemplified in the present embodiment is connected to a front frame 1 located at the front of the vehicle body, an engine 2 connected to the rear of the front frame 1, and a lower rear end of the engine 2. A clutch housing 3, an intermediate frame 4 connected to the rear end of the clutch housing 3, a rear case transmission case (hereinafter referred to as a T / M case) 5 connected to the rear end of the intermediate frame 4, Left and right front wheels 6 located on the left and right of the body frame 1, left and right rear wheels 7 located on the left and right of the T / M case 5, left and right rear fenders 8 covering the left and right rear wheels 7, and boarding located on the rear of the vehicle body The operation part 9 of a formula, etc. are provided.

  Although not shown, the power from the engine 2 is supplied from the main clutch built in the clutch housing 3 and the transmission shaft covered by the intermediate frame 4 to the main power built in the T / M case 5. It is transmitted to the transmission. The power after the shift by the main transmission is transmitted to the left and right front wheels 6 and the left and right rear wheels 7 via an auxiliary transmission built in the T / M case 5 or the like.

  As shown in FIG. 1, the driving unit 9 includes a steering wheel 10 for steering the front wheels, a driving seat 11 positioned between the left and right rear fenders 8, and the like.

  As shown in FIGS. 1 to 3, a towable working device 13 is connected to the rear portion of the T / M case 5 via a three-point link mechanism 12 provided at the rear portion of the T / M case 5 so as to be lifted and lowered. ing. The T / M case 5 includes a mechanically linked hydraulic lifting device 14 that drives the working device 13 up and down via a three-point link mechanism 12 at the rear part thereof. The three-point link mechanism 12 includes a single top link 12A, left and right lower links 12B, and the like.

  In this embodiment, a tractor to which a plow is connected is illustrated as the towed working device 13, but a disk harrow, a cultivator, a subsoiler, or the like is adopted as the towed working device 13. be able to.

  As shown in FIGS. 1 to 9, the hydraulic lifting device 14 includes left and right lift arms 15 that suspend and support the working device 13, and a hydraulic cylinder (an example of a hydraulic actuator) that drives the left and right lift arms 15 to swing up and down. ) 16, a control valve 17 for controlling the operation of the hydraulic cylinder 16, a height setting lever 18 for setting the control target height of the work device 13, and a first link for interlocking the spool 17A of the control valve 17 with the height setting lever 18 A mechanism 19, a feedback link mechanism 20 that links the spool 17A to the left and right lift arms 15, a load detection member 21 that swings back and forth according to the traction load, a second link mechanism 22 that links the spool 17A to the load detection member 21, and a spool A sensitivity adjustment mechanism 23 that adjusts the operation sensitivity when 17A is interlocked with the load detection member 21 is provided.

  As shown in FIGS. 1 to 6, the left and right lift arms 15 swing integrally in the vertical direction with a left and right support shaft 24 provided at the upper rear end of the T / M case 5 as a fulcrum. The hydraulic cylinder 16 is integrally provided at the rear upper part of the T / M case 5.

  The control valve 17 is positioned at the right upper portion of the rear upper portion inside the T / M case 5. The control valve 17 incorporates a biasing means (not shown) for biasing the spool 17A back to the lowered position on the front side of the vehicle body. The control valve 17 includes a balance arm 26 that swings in the front-rear direction about a left-right support shaft 25 that moves integrally with the spool 17A.

  The height setting lever 18 is located on the right side of the driver seat 11. The height setting lever 18 swings back and forth with a left and right lever support shaft 27 as a fulcrum. The height setting lever 18 is oscillated and displaced in the high position setting direction by a backward pulling operation. The lever support shaft 27 is fixed to a support plate 28 attached to the right side portion of the T / M case 5. The lever support shaft 27 includes a friction-type first holding mechanism 29 that holds the height setting lever 18 at an arbitrary operation position.

  The first link mechanism 19 contacts the height setting lever 18 from the high position setting side (vehicle body rear side) of the height setting lever 18, and the first swing arm 30 swings. A first crankshaft 31 extending from the center to the upper end of the balance arm 26 is provided. The first link mechanism 19 resists the action of the urging means by the first swing arm 30 swinging in the high setting direction in conjunction with the swing operation of the height setting lever 18 in the high setting direction. Thus, the spool 17A of the control valve 17 is operated from the neutral position to the raised position. The first link mechanism 19 allows the control valve 17 to move from the neutral position to the lowered position by the action of the urging means in conjunction with the swing operation of the height setting lever 18 in the lower position setting direction. .

  The first swing arm 30, together with the balance arm 26, is positioned between the T / M case 5 and the right rear fender 8. The first crankshaft 31 has a central shaft portion 31A serving as a swing fulcrum of the first swing arm 30, and an L-shaped linkage shaft portion 31B extending upward from the left end of the central shaft portion 31A. ing. The central shaft portion 31 </ b> A is rotatably supported by the right side wall portion of the T / M case 5 and the support plate 28. The linkage shaft portion 31B is located inside the T / M case 5 and swings integrally with the first swing arm 30 with the central shaft portion 31A as a fulcrum.

  The balance arm 26 has a first recess 26A that is recessed from the upper end of the balance arm 26 toward the support shaft 25, and a second recess 26B that is recessed from the lower end of the balance arm 26 toward the support shaft 25. ing. The linkage shaft portion 31B of the first crankshaft 31 has a laterally extending end portion 31a. The extended end portion 31a enters the first recess 26A of the balance arm 26 in a state in which it can be displaced with respect to the balance arm 26 within the depth range of the first recess 26A.

  The first swing arm 30 extends upward from the central shaft portion 31 </ b> A of the first crankshaft 31. The first swing arm 30 includes a cam portion 30A extending forward. The front edge 30a of the cam portion 30A is in contact with the operation tool 50 provided on the height setting lever 18 from the rear side of the vehicle body.

  The feedback link mechanism 20 includes a linkage rod 32 extending from the right lift arm 15 to the front side of the vehicle body, a second swing arm 33 interlocking with the left and right lift arms 15 via the link rod 32, and a second swing arm. And a second crankshaft 34 extending from the swing center of 33 to the lower end of the balance arm 26. The feedback link mechanism 20 operates the spool 17A of the control valve 17 from the raised position or the lowered position to the neutral position in conjunction with the arrival of the work device 13 at the control target height.

  The linkage rod 32 and the second swing arm 33 are located between the T / M case 5 and the right rear fender 8. The second crankshaft 34 has a central shaft portion 34A serving as a swing fulcrum of the second swing arm 33, and an L-shaped linkage shaft portion 34B extending downward from the left end of the central shaft portion 34A. ing. The central shaft portion 34 </ b> A is rotatably supported at the right side wall portion of the T / M case 5 and the lower portion of the first crankshaft 31 in the support plate 28. The linkage shaft portion 34B is located inside the T / M case 5 and swings integrally with the second swing arm 33 with the central shaft portion 34A as a fulcrum.

  The linkage shaft portion 34B of the second crankshaft 34 has a laterally extending end portion 34a. The extended end portion 34a enters the second recess 26B of the balance arm 26 in a state in which it can be displaced with respect to the balance arm 26 within the depth range of the second recess 26B.

  The second swing arm 33 extends upward from the central shaft portion 34 </ b> A of the second crankshaft 34 through the rear of the first crankshaft 31. The extending end of the second swing arm 33 is connected to the front end of the linkage rod 32.

  The balance arm 26 is interlocked with the swinging operation of the height setting lever 18 in the high position setting direction, with the extended end portion 34a of the second crankshaft 34 as a fulcrum, and on the lift position side (rear side of the vehicle body) of the spool 17A. ). The balance arm 26 is extended by the action of the urging means provided in the control valve 17 in conjunction with the swinging operation of the height setting lever 18 in the lower setting direction (front side of the vehicle body). Using the portion 34a as a fulcrum, the spool 17A swings and displaces to the lowered position side (vehicle body front side). The balance arm 26 swings and displaces toward the lowered position side of the spool 17A with the extended end portion 31a of the first crankshaft 31 as a fulcrum in conjunction with the upward and downward swing of the left and right lift arms 15. The balance arm 26 swings and displaces toward the ascending position of the spool 17A with the extended end portion 31a of the first crankshaft 31 as a fulcrum in conjunction with the downward swing of the left and right lift arms 15.

With the above configuration, when the height setting lever 18 is swung in the high position setting direction, the height setting lever 18 presses the first rocking arm 30 in the high position setting direction, thereby the first rocking arm. 30, the linkage shaft portion 31 </ b> B of the first crankshaft 31 swings and displaces in the same high position setting direction as the height setting lever 18 with the central shaft portion 31 </ b> A of the first crankshaft 31 as a fulcrum. Then, in conjunction with this swing displacement, the balance arm 26 swings and displaces toward the rising position side of the spool 17A with the extended end portion 34a of the second crankshaft 34 as a fulcrum, and the spool of the control valve 17 17A is operated to the raised position against the action of the biasing means. As a result, the left and right lift arms 15 are swung upward and the working device 13 is raised (see FIG. 5).
When the left and right lift arms 15 are swung upward, the second crankshaft 34 and the second swing arm 33 are controlled with the central shaft portion 34A of the second crankshaft 34 as a fulcrum in conjunction with the upward swing. The spool 17A of the valve 17 is oscillated and displaced in the downward operation direction for operating the spool 17A to the downward position side. Then, in conjunction with this swing displacement, the balance arm 26 swings and displaces toward the lowered position side of the spool 17A with the extended end portion 31a of the first crankshaft 31 as a fulcrum.
At this time, if the swing operation of the height setting lever 18 in the high position setting direction is continued, the height setting lever 18 presses the first swing arm 30 in the high position setting direction, as described above. The balance arm 26 swings and displaces toward the ascending position of the spool 17A with the extended end portion 34a of the second crankshaft 34 as a fulcrum. As a result, the balance arm 26 swings counterclockwise as viewed from the right side of the vehicle body with the support shaft 25 as a fulcrum, thereby maintaining the spool 17A of the control valve 17 in the raised position. Can do. As a result, while the height setting lever 18 is being swung in the high position setting direction, the left and right lift arms 15 can be lifted and swung, and the work device 13 can be lifted.
Thereafter, when the swinging operation of the height setting lever 18 in the high position setting direction is finished and the height setting lever 18 is held at an arbitrary operation position, together with the first swinging arm 30 in conjunction therewith. The linkage shaft portion 31B of the first crankshaft 31 stops swinging and is held in a swinging posture corresponding to the holding position of the height setting lever 18, thereby extending the end portion of the second crankshaft 34. The balance arm 26 is prevented from swinging about 34a as a fulcrum. Then, only the swinging displacement of the balance arm 26 toward the lowering position with the extended end portion 31a of the first crankshaft 31 interlocked with the upward swing of the lift arm 15 as a fulcrum is performed. Then, since the spool 17A of the control valve 17 moves from the raised position to the neutral position, the left and right lift arms 15 stop rising and swinging (see FIG. 6). As a result, the work device 13 can be lifted and stopped at the control target height set by the swing operation of the height setting lever 18 in the high position setting direction.

Conversely, when the height setting lever 18 is swung in the lower setting direction, the height setting lever 18 moves away from the first swing arm 30 and the spool 17A is lowered by the action of the urging means. Allow return to position. Then, due to the action of the urging means, the spool 17A moves from the neutral position to the lowered position, whereby the left and right lift arms 15 swing downward and the work device 13 descends.
Further, the balance arm 26 swings and displaces toward the lower position of the spool 17A with the extended end portion 34a of the second crankshaft 34 as a fulcrum in conjunction with the movement from the neutral position to the lower position of the spool 17A. In conjunction with this swing displacement, the first swing arm 30 together with the linkage shaft portion 31B of the first crankshaft 31 is connected to the height setting lever 18 with the central shaft portion 31A of the first crankshaft 31 as a fulcrum. Swing and displace in the same low setting direction.
When the left and right lift arms 15 swing downward, the linkage shaft portion 34B of the second crankshaft 34, together with the second swing arm 33, links the central shaft portion 34A of the second crankshaft 34 in conjunction with the downward swing. Using the fulcrum as a fulcrum, the spool 17A of the control valve 17 is oscillated and displaced in the ascending operation direction to operate the ascending position. Then, in conjunction with this swing displacement, the balance arm 26 swings and displaces toward the spool ascending position with the extended end portion 31a of the first crankshaft 31 as a fulcrum.
At this time, if the swinging operation of the height setting lever 18 in the lower setting direction is continued, the height setting lever 18 moves in a direction away from the first swinging arm 30, as described above. The balance arm 26 swings and displaces toward the lowered position side of the spool 17A with the extended end portion 34a of the second crankshaft 34 as a fulcrum. Therefore, as a result, the balance arm 26 swings clockwise around the support shaft 25 as viewed from the right side of the vehicle body, thereby maintaining the spool 17A of the control valve 17 in the lowered position. Can do. In conjunction with the swing of the balance arm 26, the first swing arm 30 together with the linkage shaft portion 31B of the first crank shaft 31 sets the height with the central shaft portion 31A of the first crank shaft 31 as a fulcrum. The first swing arm 30 can be swung following the height setting lever 18 because the first swing arm 30 is swung in the same low setting direction as the lever 18. As a result, while the height setting lever 18 is swung in the lower setting direction, the left and right lift arms 15 are swung downward while the first rocking arm 30 is swung following the height setting lever 18. The working device 13 can be lowered.
After that, when the swinging operation of the height setting lever 18 in the lower setting direction is finished and the height setting lever 18 is held at an arbitrary operation position, the first setting arm 30 and the first swinging arm 30 are linked together. The linkage shaft portion 31B of the first crankshaft 31 stops swinging and is held in a swinging posture corresponding to the holding position of the height setting lever 18, thereby extending the end portion of the second crankshaft 34. The balance arm 26 is prevented from swinging about 34a as a fulcrum. Then, only the swinging displacement of the balance arm 26 to the rising position side with the extended end portion 31a of the first crankshaft 31 interlocked with the downward swing of the lift arm 15 is performed, and this swinging displacement is interlocked. Then, since the spool 17A of the control valve 17 moves from the lowered position to the neutral position, the left and right lift arms 15 stop moving downward. As a result, the work device 13 can be lowered and stopped at the control target height set by the swinging operation of the height setting lever 18 in the lower position setting direction.

  That is, by providing the left and right lift arms 15, the hydraulic cylinder 16, the control valve 17, the height setting lever 18, the first link mechanism 19, and the feedback link mechanism 20, the work device 13 is moved to the height setting lever 18. In conjunction with this swinging operation, position control for moving up and down to an arbitrary control target height set by the height setting lever 18 can be satisfactorily performed.

As shown in FIGS. 1 to 9 and FIG. 11, in the three-point link mechanism 12, the front end portion of the top link 12 </ b> A is connected to the upper and lower intermediate portions of the load detection member 21 via a connection pin 35 facing left and right. Further, the front end portions of the left and right lower links 12B are connected to the left and right support shafts 36 provided to the rear end portion of the T / M case 5 in the left-right direction.
With this connection structure, the traction load acts on the upper and lower intermediate portions of the load detection member 21 via the top link 12A.

  The load detection member 21 is supported by a bracket (an example of a support member) 37 fixed to the rear end of the T / M case 5 through a left and right support shaft 38 so as to be able to swing and displace in the front-rear direction. The hydraulic lifting device 14 regulates displacement of the load detection member 21 and a biasing mechanism 60 that biases the load detection member 21 in a direction against the traction load applied to the load detection member 21 (rear direction of the vehicle body). A regulating mechanism 70. The load detection member 21 is held in a reference posture extending vertically upward from the support shaft 38 by the action of the biasing mechanism 60 and the restriction mechanism 70. Then, when the traction load exceeds the set value, the load detection member 21 swings and displaces from the reference posture to the front side of the vehicle body against the action of the urging mechanism 60 in conjunction with the increase of the traction load, and In conjunction with the decrease in the traction load, the biasing mechanism 60 swings and displaces to the rear side of the vehicle body to return to the reference posture.

  The second link mechanism 22 includes an operation arm 39 that is interlocked with the load detection member 21. The operation arm 39 is supported on a U-shaped linkage part 30 </ b> B provided in the upper part of the rear end of the first swing arm 30 through a connecting pin 40 facing left and right so as to be relatively swingable. The operation arm 39 swings in the high position setting direction (rear side of the vehicle body) of the height setting lever 18 with the connecting pin 40 as a fulcrum, so that the first swing arm 30 moves from the low position setting side of the height setting lever 18. It contacts the linkage part 30B.

  In the second link mechanism 22, the operation arm 39 swings in the high position setting direction (rear side of the vehicle body) of the height setting lever 18 in conjunction with the swing of the load detection member 21 toward the vehicle body front side. By pressing the arm 30, the spool 17A of the control valve 17 is operated from the neutral position to the raised position against the action of the urging means. In the second link mechanism 22, the operation arm 39 swings in the lower setting direction (front side of the vehicle body) of the height setting lever 18 in conjunction with the swing of the load detection member 21 toward the vehicle body rear side. By moving away from the arm 30, the control valve 17 is allowed to move from the neutral position to the lowered position of the spool 17A by the action of the urging means.

  The feedback link mechanism 20 operates the spool 17A of the control valve 17 from the raised position or the lowered position to the neutral position in conjunction with the swing stop of the load detection member 21.

With the configuration described above, when the control target height is set to the work height at which the work device 13 is grounded, for example, the traction load is increased due to the working depth of the work device 13 being deepened due to the ups and downs of the field. When the traction load exceeds the set value, the load detection member 21 swings forward of the vehicle body while the traction load is rising, and in conjunction with this swing, the operation arm 39 moves the height setting lever 18 in the high position setting direction. And the first swing arm 30 is pressed in the high position setting direction. Therefore, the left and right lift arms 15 swing up and swing in the same manner as in the case where “the height setting lever 18 is swung in the high position setting direction” described above [FIG. 9).
When the left and right lift arms 15 are raised and swung, the balance arm 26 is interlocked in the same manner as described above when the left and right lift arms 15 are swung upward and downward by the swinging operation of the height setting lever 18 in the high position setting direction. However, the first end portion 31a of the first crankshaft 31 is pivotally displaced toward the lowered position side of the spool 17A with the extended end portion 31a as a fulcrum.
At this time, if the swing of the load detection member 21 to the front side of the vehicle body due to the increase in the traction load is continued, the operation arm 39 swings in the high position setting direction of the height setting lever 18 in conjunction with the swing. It moves and presses the first swing arm 30 in the high position setting direction. Therefore, the spool 17A of the control valve 17 can be maintained at the raised position in the same manner as in the case where “the swinging operation of the height setting lever 18 in the high position setting direction is continued” described above. As a result, while the load detection member 21 is swinging to the front side of the vehicle body due to the increase in the traction load, the work device 13 can be lifted together with the left and right lift arms 15, thereby reducing the set value of the traction load. The rise can be maintained within an acceptable range.
Thereafter, when the traction load becomes constant, the load detection member 21 stops swinging toward the front side of the vehicle body. In conjunction with the swing stop, the operation arm 39 stops swinging, and the first swing arm 30, the linkage shaft portion 31 </ b> B of the first crankshaft 31 is received and held in a swinging posture corresponding to the stopping posture of the load detection member 21. For this reason, the control valve 17 is operated in the same manner as in the case of “the swinging operation of the height setting lever 18 in the high position setting direction is completed and the height setting lever 18 is held at an arbitrary operation position”. The spool 17A moves from the raised position to the neutral position, and the working device 13 stops raising together with the left and right lift arms 15 (see FIG. 6).
When the traction load decreases, the load detection member 21 swings to the rear side of the vehicle body, and the operation arm 39 swings in a direction away from the first swing arm 30 in conjunction with the swing. In the same manner as in the case where the height setting lever 18 is swung in the lower position setting direction, the spool 17A is moved from the neutral position to the lowered position, and the left and right lift arms 15 are lowered and swung. Descends.
Further, the balance arm 26 swings and displaces toward the lowered position side of the spool 17A with the extended end portion 34a of the second crankshaft 34 as a fulcrum, and the first swing shaft 31B together with the linkage shaft portion 31B of the first crankshaft 31. The moving arm 30 swings and displaces in the lower setting direction of the height setting lever 18 with the central shaft portion 31A of the first crankshaft 31 as a fulcrum.
When the left and right lift arms 15 swing downward, the balance arm 26 operates in the same manner as in the case where the left and right lift arms 15 swing downward by the swinging operation of the height setting lever 18 in the lower position setting direction. However, the first crankshaft 31 swings and displaces toward the rising position of the spool with the extended end portion 31a as a fulcrum.
At this time, if the swing of the load detection member 21 toward the rear side of the vehicle body due to the decrease in the traction load is continued, the operation arm 39 swings in a direction away from the first swing arm 30 in conjunction with the swing. Therefore, the spool 17A of the control valve 17 can be maintained at the lowered position in the same manner as in the case where “the swinging operation of the height setting lever 18 in the lower setting direction is continued” described above. . Further, the first swing arm 30 can be swung following the operation arm 39. As a result, while the load detecting member 21 is swinging to the rear side of the vehicle body due to a decrease in the traction load, the working device is operated together with the left and right lift arms 15 while swinging the first swing arm 30 following the operation arm 39. 13 can be lowered, whereby the traction load can be prevented from decreasing to the set value until the load detection member 21 reaches the reference posture.
Thereafter, when the traction load decreases to the set value, the load detection member 21 returns to the reference posture and stops swinging toward the rear of the vehicle body, and the operation arm 39 stops swinging in conjunction with the swing stop. To do. Further, when the cam portion 30A of the first swing arm 30 contacts the operating tool 50 of the height setting lever 18, the linkage shaft portion 31B of the first crankshaft 31 together with the first swing arm 30 sets the height. The swinging is stopped at the swinging posture corresponding to the holding position of the lever 18. For this reason, the control valve 17 is operated in the same manner as in the case where “the swinging operation of the height setting lever 18 in the lower setting direction is completed and the height setting lever 18 is held at an arbitrary operation position” described above. The spool 17A moves from the lowered position to the neutral position, and the working device 13 stops descending together with the left and right lift arms 15. As a result, the work device 13 can be returned to the work control target height set by the height setting lever 18.
If the traction load becomes constant until the traction load is reduced to the set value, the load detection member 21 stops swinging toward the rear side of the vehicle body. However, the swinging is stopped, and the linkage shaft portion 31B of the first crankshaft 31 together with the first swinging arm 30 is received and held in a swinging posture corresponding to the stop posture of the load detecting member 21. For this reason, the control valve 17 is operated in the same manner as in the case where “the swinging operation of the height setting lever 18 in the lower setting direction is completed and the height setting lever 18 is held at an arbitrary operation position” described above. The spool 17A moves from the lowered position to the neutral position, and the working device 13 stops descending together with the left and right lift arms 15.
That is, it is possible to obtain a work height at which the work device 13 is grounded by simply adding the load detecting member 21, the second link mechanism 22, the urging mechanism 60, and the regulating mechanism 70 to the operation system for position control. During work travel with the control target height set, if the traction load exceeds the set value, the work device 13 can be automatically raised or lowered according to the traction load, thereby maintaining the traction load at the set value. The draft control can be performed satisfactorily.
As a result, it is possible to prevent a reduction in work efficiency due to slip caused by the traction load greatly exceeding the set value.

  As shown in FIGS. 1 to 10, the second link mechanism 22 includes a relay arm 41 that relays the interlocking of the operation arm 39 with the load detection member 21. The relay arm 41 swings about a swing fulcrum shaft 42 that is supported by the support member 43 on the vehicle body side so that the position can be changed.

  The sensitivity adjustment mechanism 23 includes a sensitivity adjustment lever 44 located in the operation unit 9, a linkage member 45 extending from the sensitivity adjustment lever 44 to the swing fulcrum shaft 42 of the relay arm 41, and the like. The sensitivity adjustment mechanism 23 creates a gap S between the linkage portion 30B of the first swing arm 30 and the operation arm 39 in conjunction with the change of the fixed position of the swing fulcrum shaft 42 by the operation of the sensitivity adjustment lever 44. The operating sensitivity when the spool 17A of the control valve 17 is interlocked with the load detection member 21 is adjusted (see FIGS. 4 and 10).

With the above configuration, the traction load exceeds the set value and the load detection member 21 moves toward the front of the vehicle body as the clearance S between the linkage portion 30B of the first swing arm 30 and the operation arm 39 becomes smaller by the operation of the sensitivity adjustment lever 44. When swinging, the time required for the operation arm 39 interlocked with the load detection member 21 to contact the linkage portion 30B of the first swing arm 30 and press the first swing arm 30 is shortened.
Conversely, as the clearance S between the linkage portion 30B of the first swing arm 30 and the operation arm 39 is increased by the operation of the sensitivity adjustment lever 44, the traction load exceeds the set value and the load detection member 21 swings to the front side of the vehicle body. In this case, the time required for the operation arm 39 interlocked with the load detection member 21 to contact the linkage portion 30B of the first swing arm 30 and press the first swing arm 30 becomes longer.
That is, the smaller the gap S between the linkage portion 30B of the first swing arm 30 and the operation arm 39, the more sensitive the operating sensitivity when the spool 17A of the control valve 17 is interlocked with the load detection member 21, and the traction load is reduced. Responsiveness when the working device 13 rises beyond the set value is improved.
Conversely, as the clearance S between the linkage portion 30B of the first swing arm 30 and the operation arm 39 increases, the operating sensitivity when the spool 17A of the control valve 17 is interlocked with the load detection member 21 becomes insensitive, and the traction load However, the response when the working device 13 rises exceeding the set value is deteriorated.
As a result, for example, due to field conditions such as intense field undulations, the sensitivity of operation when the spool 17A of the control valve 17 is interlocked with the load detection member 21 becomes less sensitive as the change in the traction load becomes greater. Accordingly, it is possible to prevent a decrease in ground work accuracy due to the work device 13 frequently moving up and down and hunting.
Such adjustment of the operating sensitivity can be achieved by simply connecting the sensitivity adjusting lever 44 of the operating unit 9 to the swing fulcrum shaft 42 of the relay arm 41 via the connecting member 45. It can be done easily.

  As shown in FIGS. 2 to 4, 8, and 10, the support member 43 is fixed to the lower right portion of the seat support member 46 provided at the rear end portion of the T / M case 5. The support member 43 supports the swing fulcrum shaft 42 of the relay arm 41 so that its position can be changed in the front-rear direction by having a recess 43A that is long in the front-rear direction from the front end of the support member 43 toward the rear.

  The sensitivity adjustment lever 44 is located on the right side of the driver seat 11 together with the height setting lever 18. The sensitivity adjustment lever 44 swings back and forth about a lever support shaft 27 common to the height setting lever 18. The sensitivity adjustment lever 44 has a left and right support shaft portion 44 </ b> A for connection with the linkage member 45 on the proximal end side close to the lever support shaft 27. The lever support shaft 27 includes a friction-type second holding mechanism 47 that holds the sensitivity adjustment lever 44 at an arbitrary operation position on the base side close to the support plate 28.

As shown in FIGS. 2 to 10, the relay arm 41 is provided in the second link mechanism 22 in a vertical posture in which the relay arm 41 swings back and forth with a swinging fulcrum shaft 42 facing left and right as a fulcrum.
Thereby, for example, compared with the case where the relay arm 41 is provided in a horizontal orientation in which the relay arm 41 swings back and forth with the vertical swing fulcrum shaft 42 as a fulcrum, the left and right width of the space required for the relay arm 41 is reduced. can do.
As a result, the relay arm 41 can be arranged in a narrow space between the T / M case 5 and the right rear fender 8 together with the operation arm 39 and the like.

As shown in FIG. 2, the relay arm 41 is provided in the above-described vertical orientation in the space using the space between the right lift arm 15 and the first swing arm 30.
Thereby, the relay arm 41 can be more suitably arranged in a narrow space between the T / M case 5 and the right rear fender 8.

As shown in FIGS. 1 and 2, the load detection member 21 reduces the pitching of the working device 13 that occurs when the traction load exceeds a set value by narrowing the swing range as much as possible.
Thereby, the fall of the ground work precision resulting from the pitching of the working device 13 can be suppressed while being able to mechanically detect the traction load.

  As shown in FIGS. 2, 3, and 7, the load detection member 21 has a linkage portion 21 </ b> A that extends outward from the free end portion of the load detection member 21. The link portion 21 </ b> A is provided at a position higher than the connection point of the load detection member 21 with the top link 12 </ b> A. As a result, it is possible to easily detect the swing displacement of the load detection member 21 with a small swing displacement amount accompanying the fluctuation of the traction load mechanically.

  As shown in FIGS. 2 to 6, the first swing arm 30 is positioned at a low position adjacent to the swing fulcrum side of the height setting lever 18. This facilitates direct interlocking with the height setting lever 18 while reducing the size of the first swing arm 30.

As shown in FIGS. 2 to 10, the relay arm 41 swings in the longitudinal direction with the swinging fulcrum shaft 42 as a fulcrum in the above-described vertical orientation. The second link mechanism 22 includes a first linkage member 48 extending from the linkage portion 21A of the load detection member 21 to the upper end portion of the relay arm 41, and a second linkage member 49 extending from the lower end portion of the relay arm 41 to the operation arm 39. Yes.
As a result, it is desirable that the link detecting portion 21A with the second link mechanism 22 be higher than the connection point with the top link 12A, and the lower position adjacent to the swing fulcrum side of the height setting lever 18. The first swing arm 30, which is preferably arranged, is mechanically linked via the second link mechanism 22, and the linkage position of the second link mechanism 22 relative to the load detection member 21 and the first swing arm 30 relative to the first swing arm 30 are arranged. Regardless of the height difference from the linkage position of the two-link mechanism 22, it can be smoothly linked.

The first linkage member 48 is located on the left side of the relay arm 41, and the front end portion of the first linkage member 48 is connected to the upper end portion of the relay arm 41 from the left side of the relay arm 41. The second linkage member 49 is located on the right side of the relay arm 41, and the rear end portion of the second linkage member 49 is connected to the lower end portion of the relay arm 41 from the right side of the relay arm 41.
As a result, the operating force acting on the relay arm 41 during the draft control can be applied to the relay arm 41 in a state where the relay arm 41 is distributed to the left and right of the relay arm 41. Can be.

  As shown in FIGS. 2, 3, 7, and 11, the bracket 37 includes left and right boss members 51 that support the support shaft 38 on the back portion on the lower end side. The load detection member 21 includes a cylindrical fitting portion 21 </ b> B that is fitted to the support shaft 38 so as to be relatively rotatable between the left and right boss members 51 at the lower end portion thereof. The load detection member 21 is supported by the bracket 37 so as to be swingable and displaceable by the fitting portion 21 </ b> B being supported by the left and right boss members 51 via the support shaft 38.

The urging mechanism 60 includes a compression spring (an example of a coil spring) 61 that allows a swing displacement of the load detection member 21 according to the traction load when the traction load exceeds a set value.
Accordingly, when the front end portion of the compression spring 61 is connected to the bracket 37 and the rear end portion of the compression spring 61 is connected to the load detection member 21, the traction load acting on the load detection member 21 exceeds the set value. In response to this, the load detection member 21 swings and displaces to the front of the vehicle body in response to the traction load, and the spool 17A of the control valve 17 is displaced from the neutral position to the ascending position in conjunction with this swinging displacement. With this displacement, the working device 13 rises and the traction load decreases. When the traction load decreases and becomes smaller than the elastic force of the compression spring 61, the load detecting member 21 swings and displaces to the rear side of the vehicle body by the elastic force of the compression spring 61, and the control valve is interlocked with the swing displacement. The 17 spools 17A are displaced from the raised position to the lowered position, and the displacement of the spool 17A at this time lowers the working device 13 and raises the traction load.
That is, the working device 13 can be raised and lowered appropriately according to the traction load by a simple assembly in which the compression spring 61 is connected to the bracket 37 and the load detection member 21.

The urging mechanism 60 is disposed between the bracket 37 and the free end portion of the load detection member 21.
Thereby, for example, the position of the urging mechanism 60 is moved from the oscillating fulcrum of the load detecting member 21 as compared with the case where the urging mechanism 60 is provided between the bracket 37 and the oscillating fulcrum side of the load detecting member 21. By leaving, the compression spring 61 provided in the biasing mechanism 60 without changing the set value described above can be employed as a light spring that is light and easy to handle with a small spring constant.
Further, as described above, the traction load acts on the upper and lower intermediate portions of the load detection member 21 via the top link 12A, whereas the urging mechanism 60 acts on the free end portion of the load detection member 21. As compared with the case where the traction load acts on the free end portion of the load detection member 21, a light and easy to handle inexpensive weak spring with a small spring constant can be adopted as the compression spring 61 provided in the biasing mechanism 60. .

  The urging mechanism 60 includes a holder 62 that surrounds the front side of the compression spring 61 and holds the compression spring 61. The holder 62 is disposed at the upper end portion of the bracket 37. The load detection member 21 includes a spring receiving portion 21 </ b> C that is pressed by a compression spring 61 at an upper end portion serving as a free end portion thereof. With this configuration, the urging mechanism 60 is disposed between the bracket 37 and the free end portion of the load detection member 21.

The holder 62 includes a cylindrical first member 63 joined to the upper end portion of the bracket 37 and a circular second member 64 joined to the front end of the first member 63. The first member 63 is fitted into a through hole 37 a formed at the upper end portion of the bracket 37, and the front and rear intermediate sides of the first member 63 are joined to the bracket 37.
Thereby, the urging mechanism 60 can be disposed forward using the space above the T / M case 5, and as a result, the urging mechanism 60 and the load detection member 21 are unnecessary to the rear side of the vehicle body. Can be prevented from overhanging.

The restriction mechanism 70 is disposed at a position between the support shaft 38 and the biasing mechanism 60 between the bracket 37 and the load detection member 21.
In other words, the restriction mechanism 70 is made using the space between the support shaft 38 and the urging mechanism 60 formed by arranging the urging mechanism 60 between the bracket 37 and the free end portion of the load detection member 21. Thus, the load detecting member 21 is unnecessary while preventing the enlargement caused by disposing the restricting mechanism 70 at a position deviated from between the support shaft 38 and the urging mechanism 60. Displacement can be prevented.

The regulation mechanism 70 includes left and right elongated holes 37b formed in the bracket 37 so as to extend in the displacement direction of the load detection member 21, and a pin 71 equipped in the state where the load detection member 21 is inserted into the left and right elongated holes 37b. It has.
That is, it is possible to reliably prevent unnecessary displacement of the load detection member 21 with a simple configuration in which the bracket 37 is provided with the left and right elongated holes 37b and the load detection member 21 is provided with the pin 71.

  The left and right elongated holes 37 b are formed in the left and right support members 52 joined to the back surfaces of the upper and lower intermediate portions of the bracket 37. The pin 71 is supported by the left and right side wall portions 21D extending between the fitting portion 21B and the spring receiving portion 21C in the load detection member 21.

As shown in FIGS. 2 and 11, the urging mechanism 60 has a spring force adjustment unit 65 that allows a setting value that allows the load detection member 21 to swing and displace to the front side of the vehicle body in accordance with the traction load. It has.
Thereby, the operator can change the setting value mentioned above according to the hardness of the soil of the work place which influences traction load, etc.
As a result, draft control suitable for the work place can be performed.

The spring force adjusting portion 65 prevents loosening of the bolt-attaching through-hole 64 a provided in the center of the second member 64 and the welding nut 66, the adjusting bolt 67 screwed into the welding nut 66, and the adjusting bolt 67. A locking nut 68 and a circular spring receiving member 69 disposed inside the first member 63 so as to be position-changeable are provided.
With this configuration, the operator adjusts the screwing amount of the adjustment bolt 67 screwed and attached to the welding nut 66 and changes the receiving position of the compression spring 61 by the spring receiving member 69, whereby the elastic force of the compression spring 61 is changed. Can be adjusted, and the set value described above can be changed.

As shown in FIGS. 2, 4 to 6, 9, and 10, the front edge 30 a of the cam portion 30 </ b> A in the first swing arm 30 is accompanied by the swing operation of the height setting lever 18 in the high position setting direction. The portion of contact with the operating tool 50 that is displaced in this manner is formed in an arcuate shape that contacts the operating tool 50 in a state close to a state orthogonal to the moving direction of the operating tool 50.
Thereby, for example, compared with the case where the front edge 30a of the cam portion 30A is formed in a straight line, the swinging operation of the height setting lever 18 in the high position setting direction is performed with respect to the operation tool 50 of the height setting lever 18. Thus, the occurrence of inconvenience that the operating force transmitted from the operating tool 50 of the height setting lever 18 to the cam portion 30A of the first swing arm 30 greatly changes due to the displacement of the contact portion of the cam portion 30A is suppressed. be able to.
That is, in the raising operation of the work device 13, an operation structure that presses the cam portion 30 </ b> A of the first swing arm 30 to the rear side of the vehicle body by the operation tool 50 of the height setting lever 18 is employed, and the operation required for this raising operation is performed. The force can be reduced almost uniformly.

The operation tool 50 includes a left and right fixed pin 18A fixed to the height setting lever 18, a rotating body 53 supported by the fixed pin 18A so as to be relatively rotatable.
Thus, the frictional resistance generated when the cam portion 30A of the first swing arm 30 is slidably displaced with respect to the operation tool 50 of the height setting lever 18 as the swing operation of the height setting lever 18 is performed. It can be effectively reduced.
As a result, the operator can smoothly perform the raising / lowering operation of the working device 13 by the swinging operation of the height setting lever 18 with a light operation force.
The rotating body 53 can employ a collar, a roller, a bearing, or the like.

  As shown in FIGS. 1 and 12, the driving unit 9 includes an accelerator lever 54 that can swing in the front-rear direction at a position to the lower right of the steering wheel 10. The driving unit 9 includes an operation panel 55 below the steering wheel 10. The accelerator lever 54 passes through an accelerator lever opening 55 a formed on the right side of the operation panel 55, and the free end side of the accelerator lever 54 is located on the right outer side of the operation panel 54.

The accelerator lever 54 has a swing fulcrum portion 54 </ b> A connected to an accelerator operating rotation shaft 56 inside the operation panel 55. The accelerator lever 54 is provided with a rubber cover member 57 that covers the accelerator lever opening 55a at a position adjacent to the accelerator lever opening 55a on the free end side so as to be able to swing integrally. The cover member 57 has a wide cover region that can cover the accelerator lever opening 55a regardless of the integral swinging with the accelerator lever 54.
Accordingly, the cover member 57 is covered with the accelerator lever opening 55a without providing the bellows part that allows the accelerator lever 54 to swing, as compared with the configuration in which the cover member 57 is fixed to the operation panel 55. Can do.
Further, there is a problem that the cover member 57 is detached from the operation panel 55 and the accelerator lever opening 55a is exposed when the accelerator lever 54 is swung, which may occur in the configuration in which the cover member 57 is fixed to the operation panel 55. It can be avoided.

[Another embodiment]
The present invention is not limited to the configuration exemplified in the above-described embodiment, and typical other embodiments relating to the present invention will be exemplified below.

[1] The tractor may adopt the following configuration.
For example, the tractor may be configured to have a crawler specification including left and right crawlers instead of the left and right rear wheels 7.
For example, the tractor may be configured in a full crawler specification including left and right crawlers instead of the left and right front wheels 6 and the left and right rear wheels 7.
For example, the tractor may be configured to have an electric specification including an electric motor instead of the engine 2.
For example, the tractor may be configured in a hybrid specification including the engine 2 and an electric motor.

[2] A hydraulic motor or the like may be employed as the hydraulic actuator 16.

[3] The control valve 17 may include a biasing means for biasing the spool 17A back to the lowered position outside the control valve 17.

[4] The load detection member 21 can be variously modified.
For example, the load detection member 21 may be configured such that the upper end portion thereof is supported by the support member 37 via the support shaft 38.
For example, the load detection member 21 may be configured to be supported by the support member 37 via a vertically supporting shaft 38 so as to be able to swing and displace.
For example, the load detection member 21 may be configured to be supported by the support member 37 so as to be slidable in the front-rear direction.

[5] The configuration of the urging mechanism 60 can be variously changed.
For example, the urging mechanism 60 may include a tension spring or a torsion spring as the coil spring 61.
For example, the urging mechanism 60 may be configured without the spring force adjusting unit 65.
For example, the urging mechanism 60 may be configured to include a plurality of coil springs 61.
For example, the urging mechanism 60 may be configured such that the holder 62 is mounted on the load detection member 21 and the spring receiving portion 21 </ b> C is mounted on the support member 37.

[6] The urging mechanism 60 may be disposed between the support member 37 and the swing fulcrum side of the load detection member 21.

[7] The configuration of the link mechanism 22 can be variously changed.
For example, the link mechanism 22 may have a configuration in which the operation arm 39 is supported by the first swing arm 30 through a vertically connecting pin 40 so as to be relatively swingable.
For example, the link mechanism 22 may be configured to include a V-shaped relay arm 41.
For example, the link mechanism 22 may have a configuration in which the relay arm 41 is provided in a lateral orientation in which the relay arm 41 swings back and forth with the upward and downward swing fulcrum shaft 42 as a fulcrum.
For example, in the link mechanism 22, the first linkage member 48 is positioned on the right side of the relay arm 41 provided in the vertical orientation, and the front end portion of the first linkage member 48 extends from the right side of the relay arm 41 to the upper end of the relay arm 41. And the second linkage member 49 is positioned on the left side of the relay arm 41, and the rear end portion of the second linkage member 49 is connected to the lower end of the relay arm 41 from the left side of the relay arm 41. It may be a configuration.
For example, the link mechanism 22 is configured such that the first linkage member 48 and the second linkage member 49 are positioned on the left and right sides of the relay arm 41 provided in the vertical orientation, and the first linkage member 48 and the second linkage member 49 are A configuration in which the relay arm 41 is connected to the relay arm 41 from the left or right side of the relay arm 41 may be employed.

[8] The restriction mechanism 70 includes left and right elongated holes 37b formed in the displacement direction of the load detecting member 21 in the load detecting member 21, and a pin 71 inserted in the left and right elongated holes 37b in the bracket 37. It may be.

[9] The regulation mechanism 70 may be provided on the swing fulcrum side or the free end side of the load detection member 21 between the support member 37 and the load detection member 21.

[10] The configuration of the spring force adjusting unit 65 can be variously changed according to the type of the coil spring 61 to be employed and the number of the coil springs 61 to be used.

  The present invention can be applied to a tractor including a mechanical draft control system that raises and lowers a towed working device according to a tow load.

DESCRIPTION OF SYMBOLS 13 Working apparatus 15 Lift arm 16 Hydraulic actuator 17 Control valve 17A Spool 21 Load detection member 22 Link mechanism 37 Support member 37b Long hole 38 Support shaft 60 Energizing mechanism 61 Coil spring 65 Spring force adjustment part 70 Restriction mechanism 71 Pin

Claims (5)

A lift arm that suspends and supports a tow-type work device, a hydraulic actuator that swings and drives the lift arm in a vertical direction, a control valve that controls the operation of the hydraulic actuator, and a support member that is fixed to the rear of the vehicle body A load detecting member supported so as to be displaceable, an urging mechanism for urging the load detecting member in a direction against a traction load applied to the load detecting member, and a spool of the control valve linked to the load detecting member A link mechanism
The urging mechanism includes a coil spring that allows a displacement of the load detection member according to the traction load when the traction load exceeds a set value. The load detection member is supported by the support member so as to be able to swing and displace via a support shaft,
The tractor according to claim 1, wherein the urging mechanism is disposed between the support member and a free end portion of the load detection member. A regulation mechanism for regulating displacement of the load detection member;
The tractor according to claim 2, wherein the restriction mechanism is disposed at a position between the support shaft and the biasing mechanism between the support member and the load detection member.   The regulation mechanism is inserted into the elongated hole formed in one of the support member and the load detection member so as to be long in the displacement direction of the load detection member, and the other of the support member and the load detection member. The tractor according to claim 3, further comprising a pin equipped in a mounted state.   The tractor according to any one of claims 1 to 4, wherein the urging mechanism includes a spring force adjusting unit that enables the setting value to be changed.

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