JP2017063686A - Tractor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a configuration, improve operation ability, and perform draft control in which sensitivity can be adjusted.SOLUTION: A tractor performs position control by actions of a first link mechanism 19 for linking a spool 17A of a control valve 17 to a height setting lever 18 and a feedback link mechanism 20 for linking the spool 17A to a lift arm 15, and performs draft control by actions of a second link mechanism 22 for linking the spool 17A to a load detection member 21, and the feedback link mechanism 20. A sensitivity adjustment mechanism 23 changes a gap S between an oscillation arm 30 of the first link mechanism 19 and an operation arm 39 of the second link mechanism 22, in linkage to an operation of a sensitivity adjustment lever 44 located on an operation part, for adjusting operation sensitivity of the spool 17A in the draft control.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a lift arm that suspends and supports a towed 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 spool of the control valve Urging means for urging return to the lowered position, a height setting lever for setting a control target height of the working device, a first link mechanism for interlocking the spool with the height setting lever, and the spool A feedback link mechanism that interlocks with the lift arm, a load detection member that moves back and forth in response to a traction load, a second link mechanism that interlocks the spool with the load detection member, and the spool that interlocks with the load detection member. The present invention relates to a tractor provided with a sensitivity adjustment mechanism that changes operating sensitivity at the time.

  As the tractor as described above, a lift arm that suspends and supports a tow-type work device (cultivation device), a hydraulic actuator (hydraulic cylinder) that drives the lift arm to swing up and down, and a control that controls the operation of the hydraulic actuator Valve (hydraulic control valve), biasing means (coil spring) for biasing the spool of the control valve to the lowered position, height setting lever (elevating operation lever) for setting the control target height of the work device, A first link mechanism (such as a swing arm and an operation arm) that links the spool to the height setting lever, a feedback link mechanism (such as a feedback link and a feedback arm) that links the spool of the control valve to the lift arm, and the like are provided. In conjunction with the operation of the height setting lever, Is that so as to perform the position control to position the constant has been controlled target height (for example, see Patent Document 1).

  In another tractor, a lift arm that suspends and supports a towed work device (plow or tillage device, etc.), a hydraulic actuator (hydraulic cylinder) that drives the lift arm to swing up and down, and a hydraulic actuator are operated. Control valve (control valve) to be controlled, biasing means (biasing spring) for biasing the spool of the control valve in the neutral position direction, height setting lever (position lever) for setting the control target height of the work device, control First link mechanism (arm shaft, arm, etc.) that links the valve spool (main spool) to the height setting lever, and feedback link mechanism (position feedback link mechanism) that links the control valve spool to the lift arm, etc. The height of the work device is linked to the operation of the height setting lever. Is that so as to perform the position control to position the control target height set at a constant lever (for example, see Patent Document 2).

  In the tractor described in Patent Document 2, a draft adjustment lever for setting a tilling depth, a link mechanism (such as a cylinder shaft and an arm) for interlocking the spool of the control valve with the draft adjustment lever, and a forward / backward swing according to the traction load. The load detecting member (top link hinge) that moves, and the second link mechanism (draft feedback link mechanism) that interlocks the spool of the control valve with the load detecting member, etc. Draft control is maintained to maintain the set value determined by the setting.

  Further, in the tractor described in Patent Document 2, a traction buffer mechanism for buffering the compressive load and the tensile load applied to the top link during the traction operation is interposed between the load detection member and the body side of the tractor. . The traction buffer mechanism includes a set bolt that extends between the machine body and the load detection member, and a balance spring that is externally fitted to the set bolt. A sensitivity adjustment mechanism (draft sensing load adjustment mechanism) for adjusting the operation sensitivity when the spool of the control valve is interlocked with the load detection member is interposed between the load detection member and the set bolt. The sensitivity adjustment mechanism includes an adjustment bolt that is externally fitted to the set bolt so as to be relatively rotatable, and a spring holder that is screwed into the adjustment bolt. As a result, the sensitivity adjustment mechanism changes the spring load of the balance spring by moving the spring holder in the axial direction of the set bolt in conjunction with the rotation of the adjustment bolt. The operation sensitivity when the spool of the control valve is interlocked with the load detection member is adjusted.

Japanese Patent Laid-Open No. 10-38135 JP 2006-109802 A

  As with the tractor described in Patent Document 2, it is desired that the tractor described in Patent Document 1 be capable of performing draft control capable of adjusting sensitivity.

  However, in order to enable draft control, if a configuration similar to that of the tractor described in Patent Document 2 is adopted, a draft adjustment lever for setting the tillage depth and a control valve for the control valve can be used separately from the operation system for position control. Operation exclusively for draft control including a link mechanism for interlocking the spool with the draft adjustment lever, a load detection member that swings back and forth according to the traction load, and a second link mechanism for interlocking the spool of the control valve with the load detection member. Since a system is required, there is room for improvement in simplifying the configuration.

  Further, when the sensitivity adjustment mechanism similar to that of the tractor described in Patent Document 2 is provided, it is necessary to descend from the tractor when performing sensitivity adjustment, so there is room for improvement in terms of operability.

  That is, it is desired to be able to perform draft control capable of adjusting sensitivity while simplifying the configuration and improving operability.

As means for solving the above problems, the tractor according to the present invention is:
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 spool of the control valve at a lowered position Biasing means for urging return, a height setting lever for setting a control target height of the working device, a first link mechanism for interlocking the spool with the height setting lever, and the spool for the lift arm A feedback link mechanism to be interlocked, a load detection member that moves back and forth in accordance with a traction load, a second link mechanism that interlocks the spool with the load detection member, and an operation sensitivity when the spool is interlocked with the load detection member And a sensitivity adjustment mechanism that changes
When the traction load exceeds a set value, the load detection member is displaced to the vehicle body front side in conjunction with the increase in the traction load, and is displaced to the vehicle body rear side in conjunction with the decrease in the traction load. ,
The first link mechanism includes a swing arm that comes into contact with the height setting lever from a high position setting side of the height setting lever, and interlocks with a swing operation of the height setting lever in a high position setting direction. Then, the swing arm swings in the high position setting direction to operate the spool to the raised position side, and in conjunction with the swing operation of the height setting lever in the low position setting direction, Allow movement to the lowered position side,
The second link mechanism includes an operation arm that is supported by the swing arm so as to be relatively swingable, and the operation arm swings in the high position setting direction in conjunction with the movement of the load detection member toward the vehicle body front side. The spool is operated to the raised position side by moving and pressing the swing arm, and the operation arm swings in the low position setting direction in conjunction with the movement of the load detection member to the rear side of the vehicle body. And allowing the spool to move to the lowered position side by moving away from the swing arm,
The feedback link mechanism operates the spool to a neutral position in conjunction with reaching the control target height of the working device or stopping the swing of the load detection member,
The sensitivity adjustment mechanism adjusts the operation sensitivity by changing a gap between the swing arm and the operation arm in conjunction with an operation of a sensitivity adjustment lever located in the operation unit.

According to this means, when the height setting lever is swung in the high setting direction, the height setting lever presses the rocking arm, and by this pressing, the rocking arm is moved together with the height setting lever in the high setting direction. Oscillating displacement. Then, in conjunction with this swing displacement, the spool of the control valve moves to the raised position side against the action of the biasing means. As a result, the lift arm rises and swings to raise the work device.
Conversely, when the height setting lever is swung in the low setting direction, the height setting lever is separated from the rocking arm, thereby allowing the spool to move toward the lowered position. Then, the spool of the control valve moves to the lowered position side by the action of the urging means. As a result, the lift arm descends and swings to lower the working device.
After that, when the swing operation of the height setting lever is finished, the control target height of the work device is set according to the operation position of the height setting lever, and in conjunction with the work device reaching the control target height, A feedback link mechanism operates the control valve spool to the neutral position. As a result, the lift arm stops swinging, and the working device stops at the control target height.
As a result, it is possible to satisfactorily perform position control for positioning the work device at the control target height set by the height setting lever.

Further, according to this means, when the traction load exceeds the set value during the work travel in which the control target height is set to the work height at which the work device contacts the ground, the load detection member is used while the traction load is increased. Moves to the front side of the vehicle body, and in conjunction with this movement, the operating arm swings in the high setting direction and presses the swinging arm. Then, by this pressing, the swing arm is swung in the high position setting direction together with the operation arm, and in conjunction with this swing displacement, the spool of the control valve moves to the raised position side against the action of the biasing means. Moving. As a result, the lift arm swings up and down, and the work device rises from the control target height to suppress an increase in the traction load.
Thereafter, when the traction load becomes constant, the load detection member stops moving toward the front side of the vehicle body, and in conjunction with the movement stop, the feedback link mechanism operates the spool of the control valve to the neutral position. As a result, the lift arm stops rising and swinging, and the work device stops.
When the traction load decreases, the load detection member moves to the rear side of the vehicle body, and in conjunction with this movement, the operating arm swings in the low setting direction and moves away from the swinging arm, so that the spool is moved to the lowered position side. Movement is allowed. Then, the spool of the control valve moves to the lowered position side by the action of the urging means. As a result, the lift arm swings downward and the working device descends toward the control target height.
Thereafter, when the working device is lowered to the control target height, the load detection member stops moving toward the rear side of the vehicle body, and in conjunction with the movement stop, the feedback link mechanism operates the spool of the control valve to the neutral position. As a result, the lift arm stops descending and swinging, and the work device stops at the control target height. In conjunction with the movement of the spool to the neutral position, the swing arm swings and displaces in the lower setting direction, contacts the height setting lever, and is received by the height setting lever.
As a result, during work travel where the work device is grounded, the work device can be automatically raised and lowered according to the traction load if the traction load exceeds the set value, thereby maintaining the traction load at the set value. Draft control can be performed well.

  In other words, both position control and draft control should be performed satisfactorily while simplifying the configuration in which the height setting lever, feedback link mechanism, etc. are used for both the position control operation system and the draft control operation system. Can do.

Furthermore, according to this means, when the traction load exceeds the set value and the load detection member moves to the front side of the vehicle body as the clearance between the swing arm and the operation arm becomes smaller by operating the sensitivity adjustment lever, the operation arm is The time required to contact the swing arm and press the swing arm after swinging in the high setting direction in conjunction with the load detection member is shortened.
Conversely, as the clearance between the swing arm and the operating arm increases as the sensitivity adjustment lever is operated, the operating arm becomes the load detecting member when the traction load exceeds the set value and the load detecting member moves to the front side of the vehicle body. The time required from the interlocking swing in the high setting direction to the contact with the swing arm and pressing the swing arm becomes longer.
In other words, the smaller the gap between the swing arm and the operating arm, the more sensitive the operating sensitivity when the spool of the control valve is interlocked with the load detection member, and when the traction load exceeds the set value and the working device rises. Responsiveness is improved.
Conversely, the greater the clearance between the swing arm and the operating arm, the less sensitive the operating sensitivity when the control valve spool is interlocked with the load detection member, and when the traction load exceeds the set value and the work device rises. The response of becomes worse.
As a result, for example, due to the field conditions such as intense field undulations, the greater the change in the traction load, the lower the operating sensitivity, resulting in frequent lifting and hunting of the work device. It is possible to prevent a decrease in the accuracy of ground work.

  And adjustment of such an operation sensitivity can be easily performed only by operating a sensitivity adjustment lever, being in a driving part.

  Therefore, it is possible to satisfactorily perform position control and draft control capable of adjusting sensitivity while simplifying the configuration and improving operability.

As one of the means for making the present invention more suitable,
The second link mechanism includes a relay arm in a vertical orientation that swings a balance in the front-rear direction about a pivot shaft that is horizontally oriented, and a first linkage member that extends from the load detection member to an upper end portion of the relay arm. And a second linkage member extending from the lower end of the relay arm to the operation arm.

  According to this means, for example, as compared with the case where the relay arm is provided in a left-right orientation that swings back and forth with the vertical swing fulcrum shaft as a fulcrum, the lateral width of the space required for the installation of the relay arm is reduced. be able to. As a result, the relay arm can be easily deployed in a space with a narrow left and right width such as between the transmission case and the rear fender.

  In addition, according to this means, it is generally desirable that the load detecting member is arranged on the upper side of the tractor by being linked to the top link of the three-point link mechanism for connecting the working device located at the rear of the tractor. And a swing arm that is preferably disposed at a low position adjacent to the swing fulcrum side of the height setting lever, by mechanical linkage via the second link mechanism, the second link mechanism with respect to the load detection member Regardless of the height difference between the linkage position and the linkage position of the second link mechanism with respect to the swing arm, the linkage can be performed smoothly.

As one of the means for making the present invention more suitable,
The first linkage member is located on one of the left and right sides of the relay arm and connected to the upper end of the relay arm from the left and right side of the relay arm;
The second linkage member is located on the left and right side of the relay arm, and is connected to the lower end of the relay arm from the left and right side of the relay arm.

  According to this means, the operating force acting on the relay arm during draft control can be applied to the relay arm in a state where the relay arm is distributed to the left and right of the relay arm, thereby making the swing of the relay arm stable and smooth. be able to.

As one of the means for making the present invention more suitable,
The swing fulcrum shaft is supported by a support member on the vehicle body side so that the position can be changed,
The sensitivity adjustment mechanism includes a linkage member extending from the sensitivity adjustment lever to the swing fulcrum shaft, and the swing adjustment is performed in conjunction with a change in the fixed position of the swing fulcrum shaft by operation of the sensitivity adjustment lever. The gap between the arm and the operation arm is changed.

  According to this means, the operation sensitivity when the spool of the control valve is interlocked with the load detection member can be achieved with a simple configuration in which the sensitivity adjustment lever of the operation unit is linked to the swing fulcrum shaft of the relay arm via the linkage member. This can be done easily while in the driving section.

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.

  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 this embodiment includes 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 clutch connected to the lower rear end of the engine 2. A housing 3, an intermediate frame 4 connected to the rear end of the clutch housing 3, a transmission case (hereinafter referred to as a T / M case) 5 connected to the rear end of the intermediate frame 4, and a front frame 1. Left and right front wheels 6 positioned on the left and right, left and right rear wheels 7 positioned 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 a riding-type driving unit positioned on the rear of the vehicle body 9, etc.

  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 the link mechanism 12 at the rear portion 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 about a left and right support shaft 24 provided at the upper rear end of the T / M case 5. 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 of the cam portion 30A is in contact with the left and right fixing pin 18A provided to 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 lowering operation direction for operating the spool 17A to the lowering 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, in the link mechanism 12, the front end portion of the top link 12 </ b> A is connected to the upper end portion serving as the free end portion of the load detection member 21 via a connecting 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.

  The load detection member 21 is connected to a bracket 37 fixed to the rear end of the T / M case 5 through a left and right swing support shaft 38 so as to be able to swing back and forth. The load detection member 21 swings from the reference posture to the front side of the vehicle in conjunction with the increase in the traction load when the vertical posture extending upward from the swing fulcrum shaft 38 is a reference posture and the traction load exceeds a set value. It moves dynamically and swings and displaces to the rear side of the vehicle in conjunction with a decrease in the traction load to return to the reference posture. The bracket 37 is loaded by contact with the front wall portion 37A that restricts swinging of the load detection member 21 toward the front of the vehicle body by contact with the free end portion of the load detection member 21 and the free end portion of the load detection member 21. Left and right restricting portions 37B for restricting the swinging of the detection member 21 to the rear are provided. The swing fulcrum shaft 38 employs a torsion bar that allows the load detection member 21 to swing toward the front of the vehicle body when the traction load applied to the load detection member 21 via the top link 12A exceeds a set value. Has been.

  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 above-described configuration, during work travel in which the control target height is set to the work height at which the work device touches down, for example, the cultivating depth of the work device 13 is deepened due to the ups and downs of the farm field, so that the traction load is increased. When the set value is exceeded, the load detecting member 21 swings to the front side of the vehicle body while the traction load is rising, and in conjunction with this swinging, the operation arm 39 moves in the high position setting direction of the height setting lever 18. It swings and presses the first swing arm 30 in the high 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 fixing pin 18A 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.
In other words, only the load detection member 21 and the second link mechanism 22 are added to the operation system for position control, and when the control target height is set to the work height at which the work device 13 contacts the ground, When the load exceeds the set value, the work device 13 can be automatically raised and lowered according to the traction load, and thus the draft control for maintaining the traction load at the set value can be performed favorably.
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 9, 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 43. 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 9, 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 about a left and right swing fulcrum shaft 42 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 installation of 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. 1 to 3 and 7, the load detection member 21 has a long distance from the swing fulcrum shaft 38 to the connection point with the top link 12 </ b> A. The swing displacement amount can be detected linearly. This facilitates mechanical detection of 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.

[Another embodiment]
The present invention is not limited to the configuration exemplified in the above embodiment, and a typical alternative embodiment of the present invention will be exemplified below.

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

[2] The configuration of the first link mechanism 19 can be variously changed.
For example, the 1st link mechanism 19 may be the structure provided with the 1st rocking | fluctuation arm 30 which has linkage parts 30B, such as L shape or I shape, planar view.
For example, the first link mechanism 19 may have a configuration in which the first swing arm 30 extends downward from the central shaft portion 31 </ b> A of the first crankshaft 31.
For example, the first link mechanism 19 may have a configuration in which the central shaft portion 31 </ b> A of the first crankshaft 31 serving as a swing fulcrum of the first swing arm 30 is provided vertically.

[3] The configuration of the feedback link mechanism 20 can be variously changed.
For example, the feedback link mechanism 20 may be configured such that the second swing arm 33 extends downward from the central shaft portion 34A of the second crankshaft 34.
For example, the feedback link mechanism 20 may have a configuration in which the central shaft portion 34A of the second crankshaft 34 serving as a swing fulcrum of the second swing arm 33 is provided vertically.

[4] The configuration of the second link mechanism 22 can be variously changed.
For example, the second link mechanism 22 may be configured such that the operation arm 41 is supported by the first swing arm 30 so as to be relatively swingable via a vertically connecting pin 40.
For example, the second link mechanism 22 may be configured to include a V-shaped relay arm 41.
For example, the second 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 about the vertical swing fulcrum shaft 42 as a fulcrum.
For example, in the second 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 is connected to the relay arm 41 from the right side of the relay arm 41. The second linking member 49 is located on the left side of the relay arm 41, and the rear end of the second linking 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 configured.
For example, in the second link mechanism 22, the first linkage member 48 and the second linkage member 49 are positioned on one of 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. However, the structure connected to the relay arm 41 from the one side of the relay arm 41 may be sufficient.

[5] At least one of the first link mechanism 19, the feedback link mechanism 20, and the second link mechanism 22 may be provided along the upper surface of the T / M case 5.

[6] The configuration of the sensitivity adjusting mechanism 23 can be variously changed.
For example, the sensitivity adjustment mechanism 23 is operated in response to the change of the position of the first swing arm 30 with respect to the operation arm 39 by the operation of the sensitivity adjustment lever 44, and the gap between the first swing arm 30 and the operation arm 39. The configuration may be such that the operating sensitivity when the spool 17A of the control valve 17 is interlocked with the load detection member 21 is adjusted by changing S.

[7] The load detection member 21 may be provided in a hanging posture extending downward from the swing fulcrum shaft 38.

[8] The control valve 17 may be configured to include an urging means for urging the spool 17A to return to the lowered position outside the control valve 17.

  The present invention can be applied to a tractor including a link mechanism for position control, a link mechanism for draft control, and a sensitivity adjustment mechanism for draft control.

DESCRIPTION OF SYMBOLS 9 Driving | operation part 13 Towing type working device 15 Lift arm 16 Hydraulic actuator 17 Control valve 17A Spool 18 Height setting lever 19 First link mechanism 20 Feedback link mechanism 21 Load detection member 22 Second link mechanism 23 Sensitivity adjustment mechanism 30 Oscillation Arm 39 Operation arm 41 Relay arm 42 Oscillating fulcrum shaft 43 Support member 44 Sensitivity adjustment lever 45 Link member 48 First link member 49 Second link member S Gap

Claims (4)

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 spool of the control valve at a lowered position Biasing means for urging return, a height setting lever for setting a control target height of the working device, a first link mechanism for interlocking the spool with the height setting lever, and the spool for the lift arm A feedback link mechanism to be interlocked, a load detection member that moves back and forth in accordance with a traction load, a second link mechanism that interlocks the spool with the load detection member, and an operation sensitivity when the spool is interlocked with the load detection member And a sensitivity adjustment mechanism that changes
When the traction load exceeds a set value, the load detection member is displaced to the vehicle body front side in conjunction with the increase in the traction load, and is displaced to the vehicle body rear side in conjunction with the decrease in the traction load. ,
The first link mechanism includes a swing arm that comes into contact with the height setting lever from a high position setting side of the height setting lever, and interlocks with a swing operation of the height setting lever in a high position setting direction. Then, the swing arm swings in the high position setting direction to operate the spool to the raised position side, and in conjunction with the swing operation of the height setting lever in the low position setting direction, Allow movement to the lowered position side,
The second link mechanism includes an operation arm that is supported by the swing arm so as to be relatively swingable, and the operation arm swings in the high position setting direction in conjunction with the movement of the load detection member toward the vehicle body front side. The spool is operated to the raised position side by moving and pressing the swing arm, and the operation arm swings in the low position setting direction in conjunction with the movement of the load detection member to the rear side of the vehicle body. And allowing the spool to move to the lowered position side by moving away from the swing arm,
The feedback link mechanism operates the spool to a neutral position in conjunction with reaching the control target height of the working device or stopping the swing of the load detection member,
The sensitivity adjustment mechanism is a tractor that adjusts the operating sensitivity by changing a gap between the swing arm and the operation arm in conjunction with an operation of a sensitivity adjustment lever located in the operation unit.   The second link mechanism includes a relay arm in a vertical orientation that swings a balance in the front-rear direction about a pivot shaft that is horizontally oriented, and a first linkage member that extends from the load detection member to an upper end portion of the relay arm. The tractor according to claim 1, further comprising a second linkage member extending from a lower end portion of the relay arm to the operation arm. The first linkage member is located on one of the left and right sides of the relay arm and connected to the upper end of the relay arm from the left and right side of the relay arm;
3. The tractor according to claim 2, wherein the second linkage member is located on the left and right other side of the relay arm and connected to a lower end portion of the relay arm from the left and right other side of the relay arm. The swing fulcrum shaft is supported by a support member on the vehicle body side so that the position can be changed,
The sensitivity adjustment mechanism includes a linkage member extending from the sensitivity adjustment lever to the swing fulcrum shaft, and the swing adjustment is performed in conjunction with a change in the fixed position of the swing fulcrum shaft by operation of the sensitivity adjustment lever. The tractor according to claim 2 or 3, wherein a gap between the arm and the operation arm is changed.

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