tractor

Abstract

This tractor is provided with: a three-point link mechanism which is for mounting a work device 15 so as to enable same to be lifted and lowered; a hydraulic unit which is capable of operating the three-point link mechanism in an oscillatory manner; a load reception part 30 which, when the work device performs earthwork while being towed by a tractor body, moves in an in an oscillatory manner according to the towing load of the work device; and a link mechanism which transmits an operation amount to the hydraulic unit in order to execute oscillatory operation in accordance with the oscillation amount of the load reception part 30. Provided to the uppermost side of the link mechanism is an interlocking oscillation arm 31 that oscillates in conjunction with the oscillation of the load reception part 30 about an oscillation axis Q1 that is different from an oscillation axis P of the load reception part 30. The load reception part 30 is provided with a first part 51 for pressing the interlocking oscillation arm 31. The interlocking oscillation arm 31 is provided with a second part 52 that, upon coming into contact with the first part 51, is pressed by the first part 51. The contact position between the first part 51 and the second part 52 is configured to be changeable.

Description

Tractor

[0001] The present invention relates to a tractor provided with a three-point link mechanism for mounting a working device in a vertically movable manner.

[0002] For example, a three-point link mechanism is provided in the tractor disclosed in Japanese Patent Application Laid-Open No. 2018-042530 (Patent Document 1), and the three-point link mechanism is swing-operated by a hydraulic unit (referred to as a "hydraulic lifting device" in the document). When the working device is attached to the three-point link mechanism and performs ground work while being towed by the vehicle body, the working device is configured to be vertically movable according to the towing load. A load receiving portion (referred to as a "load detecting member" in the document) that receives the towing load from the working device is provided, and the load receiving portion swings according to the towing load of the working device, and transmits an operation amount for swinging the three-point link mechanism to the hydraulic unit via the link mechanism. Further, an interlocking swing arm (referred to as a "swing member" in the document) that can swing in conjunction with the load receiving portion is provided. When the load receiving portion swings more than a predetermined amount, the interlocking swing arm swings, the swing amount of the load receiving portion is amplified by the interlocking swing arm, and the operation sensitivity of the three-point link mechanism is improved.

[0003] Japanese Patent Application Laid-Open No. 2018-042530

[0004] In the tractor disclosed in Japanese Patent Application Laid-Open No. 2018-042530, the interlocking swing arm does not swing unless the load receiving portion swings more than a predetermined amount. That is, unless the towing load reaches a predetermined amount or more, the operation sensitivity of the three-point link mechanism is not improved. Therefore, there is room for improvement in improving the operation sensitivity.

[0005] An object of the present invention is to provide a tractor capable of controlling the lifting and lowering of a working device with high sensitivity according to a towing load.

[0006] The tractor according to the present invention is characterized in that it is provided with a three-point linkage mechanism connected to the rear of the vehicle body so as to be able to swing up and down and to which a work device is mounted so as to be able to be raised and lowered; a hydraulic unit capable of swinging the three-point linkage mechanism; a load receiving part that swings in accordance with the towing load of the work device when the work device is towed by the vehicle body and performs work on the ground; and a linkage mechanism that transmits an amount of operation for swinging the load receiving part to the hydraulic unit according to the amount of swinging of the load receiving part, and the uppermost side of the linkage mechanism is provided with a linked swinging arm that swings in conjunction with the swinging of the load receiving part on a swinging axis different from the swinging axis of the load receiving part; the load receiving part is provided with a first part that presses the linked swinging arm; the linked swinging arm is provided with a second part that contacts the first part and is pressed by the first part, and the contact position between the first part and the second part is configured to be changeable.

[0007] According to the present invention, the load-receiving section and the linked oscillation arm each oscillate on their respective oscillation axes, and the contact position between the first and second sections can be changed. Therefore, by changing this contact position, the link mechanism can amplify the amount of oscillation of the load-receiving section. Furthermore, since the linked oscillation arm is located on the uppermost side of the link mechanism, the linked oscillation arm oscillates at the same time as the load-receiving section begins to oscillate. In this state, since the contact position between the first and second sections can be changed, the link mechanism can amplify the amount of oscillation of the load-receiving section from the moment the load-receiving section begins to oscillate. Therefore, compared to a configuration in which the linked oscillation arm does not oscillate unless the load-receiving section oscillates by a predetermined amount or more, the operational sensitivity of the three-point link mechanism is improved. As a result, a tractor capable of sensitively controlling the raising and lowering of the work device in response to the traction load can be realized.

[0008] In the present invention, it is preferable that one of the first part and the second part is a rocking member, the other of the first part and the second part is a locking part having a plurality of recesses formed therein that can receive and lock the rocking member, and the rocking member is provided with a positioning mechanism for positioning the rocking angle when engaging with the plurality of recesses.

[0009] In this configuration, the combination of the oscillating member and the locking part constitutes the combination of the first part and the second part, and the oscillating member engages with the recess of the locking part. Furthermore, when the oscillating member engages with any of the multiple recesses, the oscillating angle of the oscillating member is maintained by the positioning mechanism. As a result, the contact position between the first part and the second part is maintained without shifting to an unintended position. This makes it possible for the linked oscillating arm to more effectively amplify the amount of oscillation of the load-receiving part.

[0010] In the present invention, it is preferable that the positioning mechanism is capable of positioning the oscillating member at an angle perpendicular to the oscillating angle of the load-receiving portion.

[0011] In this configuration, the angle at which the oscillating member is positioned includes an angle perpendicular to the oscillating angle of the load-receiving portion. That is, the oscillating range of the oscillating member is set to a range close to the angle perpendicular to the oscillating angle of the load-receiving portion. As a result, the oscillating member can firmly receive the reaction force from the locking portion. This allows the oscillating member to suitably press against the locking portion. Note that the "perpendicular angle" in this invention is not limited to a strictly perpendicular angle, but also includes an approximately perpendicular angle.

[0012] In the present invention, a pin capable of engaging with the plurality of recesses is provided at the free end of the oscillating member, and a common recess is formed in the locking portion that encloses the plurality of recesses so that they are arranged in a continuous line, and it is preferable that the pin passes through the common recess and engages with any one of the plurality of recesses.

[0013] In this configuration, multiple recesses are formed in the common recess, and the pin of the oscillating member engages with these multiple recesses. Furthermore, since the pin passes through the common recess and engages with any one of the multiple recesses, the common recess is formed as a gap space between the pin and the multiple recesses. As a result, when an operator changes the oscillation angle of the oscillating member, it is possible to configure the pin to oscillate within the gap space of the common recess, making the operation of changing the oscillation angle even easier.

[0014] In the present invention, it is preferable that the link mechanism is provided with a sensitivity changing unit that operates such that the amount of displacement of the lower part of the link mechanism increases as the load receiving part swings to the side with a larger traction load.

[0015] As the towing load on the work device increases, the amount of oscillation of the load-receiving part increases. When the towing load on the work device increases, it is desirable that the work device be actively controlled to rise in order to reduce the towing load. In this configuration, as the amount of oscillation of the load-receiving part increases, the amount of displacement of the lower mechanism of the link mechanism increases. As a result, the work device is actively controlled to rise, the towing load is quickly reduced, and damage to the work device and engine stall caused by the increase in towing load are effectively prevented.

[0016] In the present invention, it is preferable that the link mechanism is provided with a link ratio changing section on the downstream side of the linked swing arm, which changes the link ratio to a link ratio change rate smaller than the link ratio change rate by the first and second sections.

[0017] This configuration allows for fine adjustment of the amount of operation relative to the hydraulic unit.

[0018] This is a right side view of a tractor with a work device attached. This is a right side view showing the draft control mechanism. This is a top view showing the draft control mechanism. This is a rear view showing the draft control mechanism. This is an exploded perspective view showing the assembly of the load receiving section and the linked oscillation mechanism. This is an exploded perspective view showing the assembly of the link mechanism. This is a cross-sectional view of the link mechanism taken along line V-V in Figure 4. This is a cross-sectional view of the link mechanism taken along line V-V in Figure 4 in comparison with Figure 7. This is an enlarged side view showing the oscillating member (first part) and the locking part (second part). This is a cross-sectional view in plan view showing the oscillating member (first part), the locking part (second part), the first coil spring and the second coil spring. This is a right side view showing the oscillation between the load receiving section and the linked oscillation mechanism. This is a right side view showing the oscillation between the load receiving section and the linked oscillation mechanism. This is a right side view showing the oscillation between the load receiving section and the linked oscillation mechanism.

[0019] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that the direction indicated by the arrow "F" in Figure 1 is the front of the tractor's direction of travel, and the direction indicated by the arrow "U" is above the tractor. In this specification, the terms "left" and "right" refer to the right and left sides when viewed from the front of the tractor's direction of travel.

[0020] The tractor shown in Figure 1 is equipped with a pair of left and right front wheels 1, a pair of left and right rear wheels 2, a front frame 3, an intermediate frame 4, a clutch housing 5, a transmission case 6, a driver's unit 7, and a pair of left and right rear fenders 8.

[0021] The pair of front wheels 1 are pivotally supported on the front frame 3 located at the front of the vehicle body, and are positioned laterally to the outside of the vehicle body than the front frame 3. The intermediate frame 4 is located behind the front frame 3. A clutch housing 5 is positioned between the front frame 3 and the intermediate frame 4, and both the front frame 3 and the intermediate frame 4 are connected to the clutch housing 5. A transmission case 6 is also connected to the rear end of the intermediate frame 4. The clutch housing 5 and the transmission case 6 also serve as the tractor's vehicle frame. In other words, the tractor's vehicle frame consists of the front frame 3, the intermediate frame 4, the clutch housing 5, and the transmission case 6.

[0022] The engine E is mounted and supported at the rear of the front frame 3, and the clutch housing 5 is connected to the lower rear end of the engine E. The pair of left and right rear wheels 2 are pivotally supported on the transmission case 6, positioned to the left and right of the transmission case 6.

[0023] Although not shown in the diagram, the clutch housing 5 houses the main clutch and the like, the intermediate frame 4 is equipped with a transmission shaft, and the transmission case 6 houses the main transmission and auxiliary transmission. The power from the engine E is then transmitted to the left and right pair of front wheels 1 and the left and right pair of rear wheels 2 via the main clutch, transmission shaft, main transmission, auxiliary transmission, and the like.

[0024] The driver's unit 7 is located at the rear of the vehicle and is configured to allow an operator to sit inside. The driver's unit 7 is equipped with a steering wheel 10 and a driver's seat 11. An operator can sit in the driver's seat 11. The steering wheel 10 is located in front of the driver's seat 11, and the operator steers the pair of front wheels 1 by manually operating the steering wheel 10. Rear fenders 8 are located on the left and right sides of the vehicle's exterior, and the rear fenders 8 cover the left and right rear wheels 2 from above. The transmission case 6 is located below the driver's seat 11. The driver's seat 11 is located between the pair of rear wheels 2 in both a plan view and a front-to-rear view.

[0025] A three-point linkage mechanism 12 is connected to the rear of the transmission case 6 so as to be able to swing up and down, and the three-point linkage mechanism 12 is configured to be able to attach a working device 15. The working device 15 shown in Figure 1 is a plow. The working device 15 may also be, for example, a rotary tiller, a disc harrow, a cultivator, a subsoiler, etc.

[0026] The three-point linkage mechanism 12 is equipped with a single top link 13 and left and right lower links 14. The lower links 14 are pivotably connected to the rear lower part of the transmission case 6 around a pivot axis Y1. A load-bearing section 30 is connected to the rear upper part of the transmission case 6, and the top link 13 is pivotably connected to the load-bearing section 30 around a pivot axis Y2. The load-bearing section 30 will be described later.

[0027] The three-point linkage mechanism 12 is driven up and down by a hydraulically driven lift arm 16. Specifically, one end of the link member 19 is pivotally connected to the tip of the lift arm 16 with a pin, and the other end of the link member 19 is pivotally connected to the lower link 14 with a pin.

[0028] The lift arm 16 is configured to swing up and down about the pivot axis X based on the drive of a hydraulic actuator (not shown). The lower link 14 swings up and down in conjunction with the up and down swing of the lift arm 16. The top link 13, which is connected to the work device 15, also swings up and down in conjunction with the up and down swing of the lower link 14. The work device 15 is connected to the top link 13 and the lower link 14 so as to be able to swing relative to each other, and the work device 15 moves up and down in conjunction with the up and down swing of the top link 13 and the lower link 14, respectively.

[0029] When the operator operates the height setting lever 23, hydraulic fluid is supplied to and discharged from the hydraulic actuator, causing the lift arm 16 to swing and the work device 15 to move up and down. The supply and discharge of hydraulic fluid is controlled by the operation of a spool (not shown). A feedback link mechanism (not shown) operates in conjunction with the up and down movement of the work device 15. The feedback link mechanism adjusts the amount of hydraulic fluid supplied to and discharged from the hydraulic actuator based on the amount of operation of the height setting lever 23 and the swing angle of the lift arm 16. When the work device 15 reaches the control target height, the supply and discharge of hydraulic fluid to the hydraulic actuator stops, and the up and down swing of the left and right lift arms 16 stops. In this way, the three-point linkage mechanism 12 mounts the work device 15 so that it can move up and down. The hydraulic actuator and spool shown in this embodiment correspond to the "hydraulic unit" of the present invention. That is, the three-point linkage mechanism 12 is equipped with a hydraulic unit that can swing.

[0030] [Regarding the Draft Control Mechanism] In this embodiment, the working height of the work device 15 is configured to be adjustable based on the working load and tilling depth when the work device 15 is working on the ground. For example, when a plow is connected to the three-point linkage mechanism 12 as the work device 15, when the plow is working on the ground, the plow receives a reaction force from the ground, and this reaction force becomes a traction load. If the traction load becomes too large, there is a risk that the plow will be damaged or the engine E will stall. For this reason, the tractor of this embodiment is equipped with a mechanism that raises and lowers the work device 15, such as a plow, according to the traction load, and adjusts the traction load to a constant level, i.e., a draft control mechanism. The draft control mechanism will be described below.

[0031] As shown in Figures 2 to 6, the draft mechanism is equipped with a load receiving section 30 and a link mechanism (a connecting oscillating arm 31, a connecting link section 32, a tilling depth adjustment cam 34, a connecting oscillating section 35, and a connecting rod 36). In order to make the load receiving section 30 and the link mechanism of the draft mechanism easier to see, the lift arm 16 is not shown in Figures 2 to 4, but the pivot axis X of the lift arm 16 is shown.

[0032] The load receiving section 30 swings in accordance with the towing load of the work device 15 when the work device 15 is towed by the tractor body while performing ground work. The link mechanism transmits the amount of operation for swinging the three-point link mechanism 12 to the hydraulic unit (including the hydraulic actuator and spool, not shown, as described above) in accordance with the amount of swing of the load receiving section 30. The link mechanism of the present invention includes a linked swing arm 31, a connecting link section 32, a tilling depth adjustment cam 34, a linked swing section 35, and a connecting rod 36.

[0033] The load-receiving section 30 is equipped with a bracket 30A, a receiving member 30B, a pivot pin 30C, a connecting pin 30D, a first coil spring 30E, a second coil spring 30F, and a swing-preventing member 30G. The bracket 30A is connected and fixed to the rear of the transmission case 6. The top link 13 is connected to the receiving member 30B.

[0034] Circular holes are drilled in the lower part of both the bracket 30A and the lower part of the receiving member 30B, through which the pivot pin 30C can be inserted, and the pivot pin 30C passes through these circular holes in the lower parts of both the bracket 30A and the receiving member 30B in a lateral direction. In other words, the pivot pin 30C pivotally connects the bracket 30A and the receiving member 30B so that they can swing relative to each other around the pivot axis P, and the receiving member 30B can swing back and forth around the pivot axis P in a lateral direction.

[0035] A round hole 30o is drilled in the upper and lower center portion of the receiving member 30B, oriented sideways to the aircraft. Similarly, an elongated hole 30p is drilled in the upper and lower center portion of the bracket 30A, oriented sideways to the aircraft. The longitudinal direction of the elongated hole 30p is aligned with the front-to-back direction of the aircraft. The connecting pin 30D passes through the round hole 30o and the elongated hole 30p in the upper and lower center portion of the receiving member 30B. Both longitudinal ends of the connecting pin 30D are located outside the receiving member 30B. A snap pin is engaged with the longitudinal end of the connecting pin 30D, preventing it from coming loose from the bracket 30A and the receiving member 30B.

[0036] The connecting pin 30D is immobile relative to the round hole 30o and is slidable along the longitudinal direction of the elongated hole 30p. As a result, the receiving member 30B can swing back and forth within the longitudinal range of the elongated hole 30p.

[0037] A storage cylinder portion 30L is formed on the upper part of the bracket 30A. The storage cylinder portion 30L is formed in a cylindrical shape facing the front and rear of the machine. The first coil spring 30E is housed in the storage cylinder portion 30L (see Figure 10). A gap is formed between the upper part of the bracket 30A and the upper part of the receiving member 30B. The first coil spring 30E is provided in this gap, and both ends of the first coil spring 30E in the direction of extension abut against the bracket 30A and the receiving member 30B, respectively. The receiving member 30B is biased by the first coil spring 30E to swing backward.

[0038] A second coil spring 30F is provided on the bracket 30A on the side opposite to the side where the first coil spring 30E is located. The elastic modulus of the second coil spring 30F is smaller than that of the first coil spring 30E. As will be described in detail later, when the first coil spring 30E is stretched and its elastic energy is released, the second coil spring 30F contracts and its elastic energy increases.

[0039] Three mounting holes 30s are drilled in the rear of the bracket 30A, and one end of the top link 13 is connected to one of the mounting holes 30s via a pin so that it can swing up and down. Of the three mounting holes 30s, the one connected to the top link 13 becomes the pivot axis Y2 of the top link 13.

[0040] The end of the top link 13 opposite to the side connected to the bracket 30A is connected to the upper part of the work device 15. Therefore, when the work device 15 is raised or when the work device 15 is not performing ground work, a tensile force acts from the work device 15 on the top link 13. In this state, a tensile force also acts from the top link 13 on the receiving member 30B, causing the receiving member 30B to swing to its furthest rearward position.

[0041] When a plow is connected to a three-point linkage mechanism 12 as a working device 15 and tilling work is being performed with the plow, the deeper the tilling depth, the stronger the reaction force the plow receives from the ground. This reaction force is a tensile load, and the upward component of the reaction force acts as a pressing force on the top link 13. This pressing force is then transmitted to the receiving member 30B via the top link 13. If this pressing force is greater than the resultant force of the elastic forces of the first coil spring 30E and the second coil spring 30F, the receiving member 30B swings forward against the resultant force of the elastic forces of the first coil spring 30E and the second coil spring 30F.

[0042] When the receiving member 30B swings forward, the first coil spring 30E contracts. The elastic force of the first coil spring 30E increases in proportion to the amount of contraction of the first coil spring 30E. Therefore, the forward swing of the receiving member 30B stops at a swing angle where the pressing force acting on the receiving member 30B due to the traction load of the work device 15 and the resultant force of the respective elastic forces of the first coil spring 30E and the second coil spring 30F are balanced. As a result, the greater the traction load due to the ground work of the work device 15, the greater the pressing force acting on the receiving member 30B, and the further forward the receiving member 30B swings. Thus, the receiving member 30B is configured to be able to detect the traction load of the work device 15.

[0043] The swing prohibition member 30G is a member that prohibits the swing of the receiving member 30B. Although not described in detail, the swing prohibition member 30G is configured to be swingable around a longitudinal swing axis V (see FIG. 4) provided at the upper left portion of the bracket 30A. A handle is provided on the upper portion of the swing prohibition member 30G. A horizontal plate portion that can be interposed in the region between the upper end portion of the bracket 30A and the upper end portion of the receiving member 30B is formed between the swing axis V and the handle. When an operator operates the handle left and right, the horizontal plate portion swings up and down. When the receiving member 30B swings to the rearmost side and the swing prohibition member 30G swings clockwise in FIG. 4, the horizontal plate portion is interposed over the entire region of the gap between the upper end portion of the bracket 30A and the upper end portion of the receiving member 30B, restricting the forward swing of the receiving member 30B. As a result, the receiving member 30B cannot swing. When the swing prohibition member 30G swings counterclockwise in FIG. 4, the horizontal plate portion moves away from the region between the upper end portion of the bracket 30A and the upper end portion of the receiving member 30B, allowing the receiving member 30B to swing back and forth.

[0044] The load receiving portion 30 is provided with an amplification adjustment portion 30H. Also, a link swing arm 31 is pivotally connected to the bracket 30A with a pin so as to be swingable back and forth. The link swing arm 31 is provided on the uppermost side of the link mechanism. The link swing arm 31 is connected to the right side portion of the bracket 30A so as to be swingable back and forth around a lateral swing axis Q1 of the machine body. The amplification adjustment portion 30H is bolt-fixed to the right side portion of the receiving member 30B. The link swing arm 31 swings in conjunction with the swing of the load receiving portion 30 around a swing axis Q1 different from the swing axis P of the load receiving portion 30.

[0045] The amplification adjustment portion 30H swings integrally with the receiving member 30B. When the receiving member 30B swings forward, the link swing arm 31 and the amplification adjustment portion 30H come into contact with each other, causing the link swing arm 31 to swing. Although details will be described later, the link swing arm 31 is configured to be able to amplify the swing amount of the receiving member 30B by swinging more greatly than the back and forth swing of the receiving member 30B. Also, although details will be described later, the amplification adjustment portion 30H is configured to be able to adjust the swing amount of the link swing arm 31.

[0046] Among the receiving member 30B, a contact bolt 30k is connected to the upper front portion with respect to the amplification adjustment portion 30H. In the state where the receiving member 30B is swung to the rearmost side, the contact bolt 30k and the interlocking swing arm 31 come into contact with each other, and the interlocking swing arm 31 and the amplification adjustment portion 30H are separated from each other. When the receiving member 30B swings forward, in the state where the contact bolt 30k and the interlocking swing arm 31 are in contact with each other, the interlocking swing arm 31 swings around the swing axis Q1. At this time, as the receiving member 30B swings forward, the separation distance between the interlocking swing arm 31 and the amplification adjustment portion 30H becomes smaller. Then, when the receiving member 30B swings further forward and the interlocking swing arm 31 and the amplification adjustment portion 30H come into contact with each other, the contact bolt 30k and the interlocking swing arm 31 are separated from each other.

[0047] As described above, the lift arm 16 (see FIG. 1, the same applies hereinafter) swings up and down by the supply and discharge of hydraulic oil to and from the hydraulic actuator, and the supply and discharge of the hydraulic oil is controlled by the operation of a spool (not shown). Each of the connecting link portion 32, the tillage depth adjustment cam 34, the interlocking swing portion 35, and the connecting rod 36 is a link mechanism for transmitting the swinging motion of the receiving member 30B to the spool.

[0048] As shown in FIGS. 2 to 6, one end portion of the connecting link portion 32 is pivotally connected to the lower end portion of the interlocking swing arm 31 by a pin member 33 so as to be relatively swingable, and the tillage depth adjustment cam 34 is pivotally connected to the other end portion of the connecting link portion 32 by a pin so as to be relatively swingable. A support member 37 is connected to the right side portion of the transmission case 6, and two cylindrical members 37A and 37B project outward from the support member 37 in the lateral direction of the machine body. The tillage depth adjustment cam 34 is supported by the cylindrical member 37B so as to be swingable back and forth around the swing axis Z1 in the lateral direction of the machine body.

[0049] As shown in Figures 6 to 8, the connecting link section 32 includes a first link member 32A, a second link member 32B, a coil spring member 32C, and a connecting pin 32D. The first link member 32A is formed by welding a flat plate member and a bolt member. One end of each of the flat plate member and the bolt member in the longitudinal direction is connected by welding. Of the flat plate member of the first link member 32A, the end opposite to the side welded to the bolt member is pivotally connected to the second link member 32B by the connecting pin 32D so as to be able to swing relative to it. The second link member 32B is a flat plate member. Of the second link member 32B, the end opposite to the side pivotally connected to the first link member 32A is pivotally connected to the tillage depth adjustment cam 34 by a pin so as to be able to swing relative to it.

[0050] A pair of nuts are locked to the upper and lower ends of the bolt member of the first link member 32A, and a coil spring member 32C and a pin member 33 are fitted between these nuts. The coil spring member 32C is positioned above the pin member 33, that is, on the side where the second link member 32B is located. The pin member 33 is fitted onto the bolt member of the first link member 32A and is inserted into one of the multiple through holes 31h formed in the lower end of the connecting swing arm 31, and is secured with a snap pin to prevent it from coming out of the through hole 31h. In other words, the lower end of the bolt member of the first link member 32A and the lower end of the connecting swing arm 31 are pivotably connected by the pin member 33.

[0051] One end of a tension spring 38 is hooked onto the tillage depth adjustment cam 34, and the other end of the tension spring 38 is hooked onto a hook member 39. The hook member 39 is supported by a cylindrical member 37A. The cylindrical member 37A is located in front of the machine body, and the tension spring 38 exerts a tensile force on both the tillage depth adjustment cam 34 and the cylindrical member 37A. As a result, the tillage depth adjustment cam 34 is biased to swing forward. The lower end of the swing arm 23A of the height setting lever 23 and the lower end of the swing arm 24A of the tillage depth lever 24 are fitted onto the cylindrical member 37A. The longitudinal direction of the cylindrical member 37A extends along the swing axis Y3 which is lateral to the machine body. The lower end of the swing arm 23A and the lower end of the swing arm 24A are each swing base ends. In other words, the height setting lever 23 and the tilling depth lever 24 can swing back and forth around the pivot axis Y3.

[0052] A cam portion 34a is formed on the tillage depth adjustment cam 34. A roller 35A is provided in the longitudinal central region of the connecting oscillation section 35, and the cam portion 34a and the roller 35A can come into contact with each other. The cam portion 34a is inclined so that it moves further away from the oscillation axis Z1 towards the front. As a result, when the front region of the cam portion 34a comes into contact with the roller 35A, the degree of oscillation of the connecting oscillation section 35 is greater compared to when the rear region of the cam portion 34a comes into contact with the roller 35A. The tillage depth adjustment cam 34 corresponds to the "sensitivity changing section" of the present invention.

[0053] As shown in Figures 7 and 8, when the tillage depth adjustment cam 34 swings backward around the pivot axis Z1 and the cam portion 34a and the roller 35A come into contact, the linked oscillation portion 35 swings backward as the roller 35A moves along the cam portion 34a. As the linked oscillation portion 35 swings backward, the cam portion 34a and the roller 35A come into contact in the front region of the cam portion 34a, so the change in the oscillation angle of the linked oscillation portion 35 becomes larger than the change in the oscillation angle of the tillage depth adjustment cam 34. In other words, the tillage depth adjustment cam 34, as a sensitivity changing portion, operates in such a way that the displacement of the lower mechanism of the link mechanism increases as the load receiving portion 30 swings towards the side with a larger traction load.

[0054] A connecting portion 34b for the control cable of the rotary tilling device is formed on the tilling depth adjustment cam 34, and one end of the control cable can be connected to the connecting portion 34b. The control cable of the rotary tilling device is described in Figures 16 and 17 of Japanese Patent Application Publication No. 2018-042530. The connecting portion 34b is located on the opposite side from the side where the cam portion 34a is located, with the connecting oscillation portion 35 in between. In automatic tilling depth control of the rotary tilling device, the vertical oscillation of the ground contact body provided on the rotary tilling device pulls the connecting portion 34b via the control cable, causing the tilling depth adjustment cam 34 to oscillate back and forth. When the control cable is connected to the connecting portion 34b, generally the oscillation prohibiting member 30G is oscillated downward, restricting the forward oscillation of the receiving member 30B. In this case, as shown in Figure 7, the first link member 32A and the second link member 32B are configured to be flexible via the connecting pin 32D, so that even if the receiving member 30B is immobile, the tillage depth adjustment cam 34 can still swing.

[0055] Multiple through holes 35h are formed in the free end of the connecting oscillation section 35, and the rear end of the connecting rod 36 is pivotally connected to one of these through holes 35h with a pin. When the connecting oscillation section 35 swings backward, the connecting rod 36 is displaced backward. Although not shown in the figures, a link mechanism that operates a spool for adjusting the supply and discharge amount of hydraulic fluid is connected to the front end of the connecting rod 36. When the connecting rod 36 is displaced backward, the spool is operated, and hydraulic fluid is supplied to the hydraulic actuator, causing the lift arm 16 to swing upward.

[0056] The pivot base end of the oscillating section 35 is pivotally connected to the free end of the bracket 24B by a pin, allowing the oscillating section 35 to swing back and forth around the pivot axis Z2. At the location of the cylindrical member 37A, the pivot base ends of the swinging arm 24A and the bracket 24B are connected by welding. The tillage depth adjustment cam 34 can also come into contact with the swinging arm 24A. When the tillage depth adjustment cam 34 swings backward, the cam portion 34a and the roller 35A come closer together, making it easier to swing the oscillating section 35 backward. In other words, when the tillage depth adjustment cam 34 swings backward, the lift arm 16 is more easily swung upward.

[0057] A torsion spring 40 is wrapped around the pivoting portion of the linked pivoting section 35. The torsion spring 40 is secured to the downward-facing portion at the pivoting base end of the linked pivoting section 35 and to the downward-facing portion at the free end of the bracket 24B. The linked pivoting section 35 is biased to pivot forward by the torsion spring 40.

[0058] When the receiving member 30B swings forward due to the pressing force from the working device 15, the oscillating arm 31 comes into contact with the contact bolt 30k or the amplification adjustment unit 30H, and the oscillating arm 31 swings clockwise in the side view in Figures 7 and 8. In conjunction with the swing of the oscillating arm 31, the connecting link unit 32 is pulled to the rear. At this time, as shown in Figure 8, the first link member 32A and the second link member 32B are pulled and straighten out, so a tensile force acts from the connecting link unit 32 to the tilling depth adjustment cam 34. As a result, the connecting link unit 32 is displaced to the rear and the tilling depth adjustment cam 34 swings to the rear.

[0059] As the tillage depth adjustment cam 34 swings, the cam portion 34a and the roller 35A move closer together. When the cam portion 34a and the roller 35A come into contact, the roller 35A moves along the cam portion 34a, causing the connecting oscillation portion 35 to swing backward. The connecting rod 36, which is pivotably connected to the connecting oscillation portion 35, is then pulled and displaced backward. The aforementioned spool is then moved, supplying hydraulic fluid to the hydraulic actuator, and the lift arm 16 swings upward in conjunction with the swing of the connecting oscillation portion 35, raising the position of the work device 15.

[0060] If the working device 15 is a plow, as the position of the plow rises, the reaction force acting on the plow from the ground decreases, and therefore the pressing force acting on the receiving member 30B via the top link 13 also decreases. When the pressing force acting on the receiving member 30B and the elastic force of the first coil spring 30E balance each other, the oscillation of the receiving member 30B, the linked oscillation arm 31, the tilling depth adjustment cam 34, and the linked oscillation section 35 stops, and the connecting rod 36 also stops being displaced. Then, the operation of the spool by the feedback link mechanism described above stops the supply and discharge of hydraulic fluid to the hydraulic actuator, and the up-and-down oscillation of the left and right lift arms 16 stops.

[0061] When the pressing force is no longer applied to the receiving member 30B, the receiving member 30B comes to rest in the position at the rearmost end of the forward and backward swing range based on the front-to-back length of the elongated hole 30p. At this time, the space between the first link member 32A and the second link member 32B in the connecting link section 32 becomes loose, so even if the oscillating arm 31 swings, the tilling depth adjustment cam 34 will no longer be linked to the swing of the oscillating arm 31. In addition, a coil spring member 32C is externally attached to the first link member 32A in the connecting link section 32. As a result, even if the receiving member 30B swings rapidly from the forward swinging position to its rearmost end, and the oscillating arm 31 also swings rapidly, the impact caused by the rapid swing is absorbed by the expansion and contraction of the coil spring member 32C. Therefore, the inconvenience of the tilling depth adjustment cam 34 and the oscillating section 35 swinging unnecessarily due to the impact is avoided. At this time, the tillage depth adjustment cam 34 swings forward due to the elastic force of the tension spring 38. Also, the linked oscillation section 35 swings forward due to the elastic force of the torsion spring 40.

[0062] [Regarding the amplification adjustment section] As described above, the linked oscillation arm 31 is configured to amplify the amount of oscillation of the receiving member 30B. In addition, the amplification adjustment section 30H is bolted to the receiving member 30B, and the amplification adjustment section 30H and the linked oscillation arm 31 are configured to be in contact with each other.

[0063] The linked oscillation arm 31 extends vertically. When the contact point between the amplification adjustment unit 30H and the linked oscillation arm 31 in the vertical direction is changed, the amount of oscillation of the linked oscillation arm 31 changes even if the amount of oscillation of the receiving member 30B remains the same. The amplification adjustment unit 30H is configured to allow adjustment of the contact point with respect to the linked oscillation arm 31 in the vertical direction.

[0064] As shown in Figures 9 to 13, the amplification adjustment unit 30H is equipped with a bracket member 50 and a swinging member 51. Elongated holes 50a are drilled in the upper and lower ends of the flat surface portion of the bracket member 50, and the pair of upper and lower elongated holes 50a extend in the vertical direction. Bolts are inserted through the pair of upper and lower elongated holes 50a. That is, the bracket member 50 is bolted to the receiving member 30B so that its vertical positioning can be adjusted. A protruding cylindrical portion 50b is formed in the region between the pair of upper and lower elongated holes 50a, and the protruding cylindrical portion 50b protrudes on the side opposite to the side where the receiving member 30B is located. A screw groove that can engage with a nut is formed at the protruding tip of the protruding cylindrical portion 50b.

[0065] The oscillating member 51 is configured to swing relative to the bracket member 50. A bolt insertion hole 51b is drilled in the swing base end of the oscillating member 51. A projection cylindrical portion 50b is inserted through the bolt insertion hole 51b, and a nut engages with the tip of the projection cylindrical portion 50b. As a result, the oscillating member 51 is configured to swing up and down around the swing axis Q2. The oscillating member 51 corresponds to the "first part" of the present invention. That is, the load receiving portion 30 is provided with a oscillating member 51 as the first part that presses against the linked swinging arm 31.

[0066] An engagement pin 51a is provided at the free end of the oscillating member 51. The engagement pin 51a is formed in a cylindrical shape that extends laterally across the machine body. The engagement pin 51a may be welded to the free end of the oscillating member 51, or it may be bolted to the free end of the oscillating member 51. The engagement pin 51a corresponds to the 'pin' of this invention.

[0067] A "second part" is provided on the oscillating arm 31 that contacts the oscillating member 51, which is the first part, and is pressed by the oscillating member 51. In this embodiment, this second part is a locking part 52. The locking part 52 has a plurality of recesses formed therein that can receive and lock the oscillating member 51. The "plural recesses" are provided on the oscillating arm 31 in the part above the oscillating axis Q1, with a first recessed part 52a, a second recessed part 52b, and a third recessed part 52c arranged vertically.

[0068] Of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c, the first recessed portion 52a is the furthest from the pivot axis Q1, and the third recessed portion 52c is the closest to the pivot axis Q1. Each of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c is formed to curve in an arc shape in correspondence with the cylindrical engagement pin 51a. As a result, each of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c is configured to receive and lock the engagement pin 51a. That is, the engagement pin 51a can engage with each of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c.

[0069] In the linked oscillating arm 31, a pair of upper and lower protruding portions 52d and 52e are formed on the upper portion of the first recessed portion 52a and the lower portion of the third recessed portion 52c, respectively. These upper and lower protruding portions 52d and 52e protrude further from the other parts of the linked oscillating arm 31 towards the side where the oscillating member 51 is located. An engagement pin 51a is positioned between these upper and lower protruding portions 52d and 52e, and the engagement pin 51a is capable of oscillating around the oscillating axis Q2 within the vertical range of these upper and lower protruding portions 52d and 52e. Between these upper and lower protruding portions 52d and 52e, the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are arranged vertically. The region enclosed like an inlet by the pair of upper and lower protruding portions 52d and 52e, the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c corresponds to the "common recess" of the present invention. That is, the locking portion 52 has a common recess that encloses a plurality of recesses arranged in a continuous line. The engagement pin 51a then passes through the common recess and engages with one of the plurality of recesses.

[0070] By swinging the oscillating member 51 up and down, the oscillating member 51 is configured to switch between a state in which the engagement pin 51a and the first recessed portion 52a can engage, a state in which the engagement pin 51a and the second recessed portion 52b can engage, and a state in which the engagement pin 51a and the third recessed portion 52c can engage. In this way, the contact position of the oscillating member 51 as the first part and the locking portion 52 as the second part can be changed.

[0071] The oscillating member 51 is equipped with a "positioning mechanism" that positions the oscillating angle when engaging with one of the first recessed portion 52a, the second recessed portion 52b, or the third recessed portion 52c. The positioning mechanism in this embodiment is a detent mechanism. The positioning mechanism is equipped with a ball 51o, a coil spring member 51p, and detent recesses 50p, 50q, and 50r.

[0072] A handle arm 51c is connected to the oscillating member 51 at a location adjacent to the bolt insertion hole 51b relative to the engagement pin 51a. The handle arm 51c protrudes on the side opposite to the receiving member 30B. A handle 51d is connected to the protruding tip of the handle arm 51c, facing backward.

[0073] The handle arm 51c is formed in a cylindrical shape. As shown in Figure 10, a cylindrical hole is drilled inside the handle arm 51c along its longitudinal direction, and a ball 51o and a coil spring member 51p for the detent mechanism are inserted into this cylindrical hole. As shown in Figures 9 and 10, detent recesses 50p, 50q, and 50r are formed in three locations on the bracket member 50 along the swing trajectory of the handle arm 51c. The ball 51o for the detent mechanism engages with one of the detent recesses 50p, 50q, or 50r. When the ball 51o engages with the detent recess 50p, the engagement pin 51a and the first recess 52a become engageable. When the ball 51o engages with the detent recess 50q, the engagement pin 51a and the second recess 52b become engageable. When the ball 51o engages with the detent recess 50r, the engagement pin 51a and the third recess 52c become engaged. In this way, the oscillating member 51 is configured to swing up and down in three stages.

[0074] In this embodiment, the positioning mechanism can position the oscillating member 51 at an angle perpendicular to the oscillation angle of the load-receiving portion 30. When the ball 51o engages with the detent recess 50q, the straight line extending from the oscillation axis P to the oscillation axis Q2 and the straight line extending from the center of the engagement pin 51a in a side view of the machine body to the oscillation axis Q2 are perpendicular or nearly perpendicular (see Figure 12). That is, the angle at which the oscillating member 51 is positioned (the oscillation angle at which the positioning mechanism positions the oscillating member 51) includes an angle perpendicular to the oscillation angle of the load-receiving portion 30. The detent recesses 50p and 50r are arranged vertically relative to the detent recess 50q. As a result, the oscillating member 51 can firmly receive the reaction force from the locking portion 52.

[0075] When no pressing force is applied to the receiving member 30B, the receiving member 30B remains stationary at the rearmost position within the forward and backward swing range based on the front-to-back length of the elongated hole 30p. At this time, the linked swinging arm 31 is in contact with the contact bolt 30k of the receiving member 30B and is separated from the swinging member 51. Therefore, when no pressing force is applied to the receiving member 30B, the operator can easily switch the swinging member 51 between the three positions described above.

[0076] As described above, when the receiving member 30B swings forward, initially the connecting swing arm 31 swings due to the contact between the contact bolt 30k and the connecting swing arm 31. The receiving member 30B swings around the swing axis P, and the connecting swing arm 31 swings around the swing axis Q1. The distance between the swinging member 51 and the swing axis P is greater than the distance between the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c and the swing axis Q1. Therefore, when the receiving member 30B swings forward while the contact bolt 30k and the connecting swing arm 31 are in contact, the displacement amounts of the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are smaller than the displacement amount of the swinging member 51. Therefore, when the receiving member 30B swings forward while the contact bolt 30k and the connecting swing arm 31 are in contact, the engagement pin 51a approaches the first recess 52a, the second recess 52b, and the third recess 52c, respectively. Then, when the engagement pin 51a comes into contact with any of the first recess 52a, the second recess 52b, or the third recess 52c, the contact bolt 30k and the connecting swing arm 31 move apart.

[0077] As shown in Figures 11 to 13, if the contact point between the rocking member 51 and the linked rocking arm 31 differs at any of the first recessed portion 52a, the second recessed portion 52b, or the third recessed portion 52c, the amount of rocking of the linked rocking arm 31 changes even if the amount of rocking of the receiving member 30B is the same. Figure 11 shows the contact state between the engagement pin 51a and the first recessed portion 52a. Figure 12 shows the contact state between the engagement pin 51a and the second recessed portion 52b. Figure 13 shows the contact state between the engagement pin 51a and the third recessed portion 52c. Note that in all of Figures 11 to 13, the rocking prohibition member 30G has been operated to a state where it does not restrict the rocking of the receiving member 30B.

[0078] The second recessed portion 52b is closer to the pivot axis Q1 than the first recessed portion 52a. Therefore, as shown in Figure 12, the amount of oscillation of the linked oscillation arm 31 when the engagement pin 51a and the second recessed portion 52b are in contact (indicated by D2) is greater than the amount of oscillation of the linked oscillation arm 31 when the engagement pin 51a and the first recessed portion 52a are in contact (indicated by D1). Therefore, when the engagement pin 51a and the second recessed portion 52b are in contact, the top link 13 oscillates up and down more than when the engagement pin 51a and the first recessed portion 52a are in contact.

[0079] The third recessed portion 52c is closer to the pivot axis Q1 than the second recessed portion 52b. Therefore, as shown in Figure 13, the amount of oscillation of the linked oscillation arm 31 when the engagement pin 51a and the third recessed portion 52c are in contact (indicated by D3) is greater than the amount of oscillation of the linked oscillation arm 31 when the engagement pin 51a and the second recessed portion 52b are in contact (indicated by D2). Therefore, when the engagement pin 51a and the third recessed portion 52c are in contact, the top link 13 oscillates up and down more than when the engagement pin 51a and the second recessed portion 52b are in contact. In this way, the greater the front-to-back oscillation of the receiving member 30B is amplified, the greater the up-and-down oscillation of the lift arm 16.

[0080] Furthermore, the angular velocity and angular acceleration of the oscillating arm 31 change in proportion to the change in the amount of oscillation of the oscillating arm 31. In other words, the angular velocity and angular acceleration of the oscillating arm 31 when the engagement pin 51a and the second recessed portion 52b are in contact is faster than the angular velocity and angular acceleration of the oscillating arm 31 when the engagement pin 51a and the first recessed portion 52a are in contact. Also, the angular velocity and angular acceleration of the oscillating arm 31 when the engagement pin 51a and the third recessed portion 52c are in contact is faster than the angular velocity and angular acceleration of the oscillating arm 31 when the engagement pin 51a and the second recessed portion 52b are in contact. When the angular velocity and angular acceleration of the oscillating arm 31 increase, the angular velocity and angular acceleration of the tillage depth adjustment cam 34 and the oscillating portion 35 also increase. Furthermore, as the angular velocity and angular acceleration of the linked oscillation section 35 increase, the speed and acceleration of the displacement of the linkage rod 36 also increase, causing the spool for controlling the supply and discharge of hydraulic fluid to be operated at high speed. When the spool is operated at high speed, the operation of the hydraulic actuator for the lift arm 16 becomes more agile, increasing the responsiveness of the lift arm 16 and increasing the angular velocity when the lift arm 16 swings. In other words, the greater the forward and backward swing of the receiving member 30B is amplified by the linked oscillation arm 31, the faster the angular velocity and angular acceleration when the lift arm 16 swings.

[0081] In this way, by changing the contact point between the oscillating member 51 and the locking portion 52, the link ratio between the receiving member 30B and the connecting oscillating arm 31 can be changed. In this embodiment, four through holes 31h are formed at the lower end of the connecting oscillating arm 31, and three through holes 35h are formed at the free end of the connecting oscillating portion 35. The through holes 31h correspond to the "link ratio changing portion" of the present invention. Similarly, the through holes 35h also correspond to the "link ratio changing portion" of the present invention.

[0082] One of the four insertion holes 31h is selected, and the pin member 33 is inserted through this hole. When the selected insertion hole 31h changes, the amount of displacement of the connecting link portion 32 changes, with the lower insertion hole 31h displacing the connecting link portion 32 more. In other words, the link ratio between the oscillating arm 31 and the connecting link portion 32 can be changed by the four insertion holes 31h. Here, the rate of change in the link ratio between the receiving member 30B and the oscillating arm 31 when the contact point between the oscillating member 51 and the locking portion 52 is changed to an adjacent upper or lower location due to the operator's switching operation of the oscillating member 51 is defined as the first link ratio change rate. Furthermore, the rate of change in the link ratio between the oscillating arm 31 and the connecting link portion 32 when the connection point with the connecting link portion 32 is changed to an adjacent insertion hole 31h among the four insertion holes 31h is defined as the second link ratio change rate. The rate of change of the second link ratio is smaller than the rate of change of the first link ratio.

[0083] One of the three through holes 35h is selected, and the rear end of the connecting rod 36 is pivotally connected to this one hole with a pin. When the selected through hole 35h changes, the amount of displacement of the connecting rod 36 changes, with the amount of displacement being greater for the free-end side through hole 31h. In other words, the link ratio between the connecting oscillation part 35 and the connecting rod 36 is configured to be changeable by the three through holes 35h. Here, the rate of change in the link ratio between the connecting oscillation part 35 and the connecting rod 36 when the connection point with the connecting rod 36 is changed to an adjacent through hole 35h is defined as the third link ratio change rate. The third link ratio change rate is smaller than the first link ratio change rate described above.

[0084] Specifically, on the downstream side of the link mechanism from the connecting swing arm 31, through holes 31h and 35h are provided as link ratio changing sections that change the link ratio to a smaller rate of change than the link ratio change rate due to the swing member 51 and the locking section 52.

[0085] [Regarding the coil spring acting on the receiving member] As shown in Figure 10, the second coil spring 30F is provided on the side opposite to the bracket 30A where the first coil spring 30E is located. The mounting structure of the second coil spring 30F will be described below.

[0086] A storage cylinder portion 30L is formed on the upper part of the bracket 30A, and the first coil spring 30E is housed in the storage cylinder portion 30L. A front-to-back oriented through hole 30q is drilled at the radial center of the front part of the storage cylinder portion 30L. A hollow boss member 60 is connected to the front part of the storage cylinder portion 30L. A screw groove is formed on the outer circumference of the front part of the boss member 60, and a nut 63 engages with this screw groove. A spacer is provided between the rear end of the boss member 60 and the nut 63, and this spacer may be composed of multiple washers (flat washers or spring washers). The nut 63 protrudes forward of the bracket 30A, and the position of the nut 63 is adjusted by the spacer. In short, the front-to-back position of the nut 63 may be adjustable to match the length of the second coil spring 30F. The nut 63 and the spacer may be a single unit, or the nut 63 may be a double nut without the spacer. Furthermore, the boss member 60 and the nut 63 may be formed as a single integral component, and the boss member 60 may not have a screw groove formed on its outer circumference at the front.

[0087] A projection 30t is welded to the area of ​​the receiving member 30B that contacts the first coil spring 30E, and a rod 61 is pivotally connected to this projection 30t so that it can swing up and down. The rod 61 passes through the inner circumferential space of the first coil spring 30E. The rod 61 passes through the hollow hole of the boss member 60 when it is fitted into the through hole 30q, and the protruding tip of the rod 61 protrudes forward of the bracket 30A.

[0088] The second coil spring 30F is externally mounted on the rod 61 on the front side of the machine body, relative to the bracket 30A. A flat washer 62, with a diameter larger than the outer diameter of the second coil spring 30F, is externally mounted on the rod 61 at the end of the second coil spring 30F opposite to the side where the receiving member 30B is located.

[0089] A screw groove is formed at the protruding tip of the rod 61. Both sides of the flat washer 62 are fastened with nuts, and the flat washer 62 is held in place by a pair of nuts. The front-to-back position of the flat washer 62 may be adjustable to match the length of the second coil spring 30F. The nut 63 is formed to have a larger opposite side diameter than the outer diameter of the second coil spring 30F. That is, both ends of the second coil spring 30F in the extension direction abut against the nut 63 and the flat washer 62, respectively. The screw groove portion of the boss member 60 and the nut that holds the flat washer 62 are formed to have an outer diameter slightly smaller than the inner diameter of the second coil spring 30F. Therefore, the screw groove portion of the boss member 60 and the nut that holds the flat washer 62 abut against the inner circumference of the second coil spring 30F without any play.

[0090] As the receiving member 30B swings back and forth, the rod 61 is displaced back and forth while swinging relative to the receiving member 30B. At this time, as the receiving member 30B swings, the rod 61 is displaced in the vertical direction, so it is necessary to prevent interference between the rod 61 and the inner circumferential surface portion of the hollow hole of the boss member 60. For this reason, the hollow hole of the boss member 60 is formed with a diameter that is sufficiently larger than the cross-sectional diameter of the rod 61.

[0091] When the receiving member 30B swings back and forth, the distance between the bracket 30A and the receiving member 30B changes, and the distance between the nut 63 supported by the bracket 30A and the flat washer 62 supported by the receiving member 30B via the rod 61 also changes. As a result, the first coil spring 30E expands and contracts. Also, when the receiving member 30B swings back and forth, the rod 61 is displaced back and forth, and the distance between the nut 63 and the flat washer 62 changes, causing the second coil spring 30F to expand and contract.

[0092] When the first coil spring 30E extends and its elastic energy decreases, the second coil spring 30F contracts and its elastic energy increases. If the pressing force suddenly ceases to act on the receiving member 30B, the elastic energy of the first coil spring 30E is released all at once, which may cause the receiving member 30B to swing rapidly from a forward-swinging state to the rearmost end of the forward-swinging range based on the front-to-back length of the elongated hole 30p. Even in such a case, as the receiving member 30B swings backward, the second coil spring 30F contracts and elastic energy is stored in the second coil spring 30F. This suppresses the rapid extension of the first coil spring 30E. As a result, the impact when the connecting pin 30D contacts the rearmost end of the elongated hole 30p is mitigated. In addition, chattering of the receiving member 30B caused by this contact is suppressed.

[0093] [Other Embodiments] The present invention is not limited to the configurations exemplified in the embodiments described above, and representative other embodiments of the present invention are described below.

[0094] (1) In the above-described embodiment, the load receiving portion 30 is provided with a rocking member 51 as the "first part," and the connecting rocking arm 31 is provided with a locking portion 52 as the "second part," but the embodiment is not limited to this. For example, the load receiving portion 30 may be provided with something equivalent to the locking portion 52, and the connecting rocking arm 31 may be provided with something equivalent to the rocking member 51. In short, one of the first part and the second part may be the rocking member 51, and the other of the first part and the second part may be the locking portion 52 which has a plurality of recesses formed that can receive and lock the rocking member 51.

[0095] (2) In the embodiment described above, the locking portion 52 as the "second part" is configured as a part of the linked swing arm 31, but the linked swing arm 31 and the locking portion 52 may be configured as separate parts.

[0096] (3) In the above-described embodiment, the load receiving portion 30 is provided with a swinging member 51 as the "first part," but the first part does not have to be a swinging member; for example, the engagement pin 51a may be configured to slide up and down. In other words, it is sufficient that the contact position between the "first part" and the "second part" can be changed.

[0097] (4) The connecting link portion 32 shown in the above-described embodiment includes a first link member 32A, a second link member 32B, a coil spring member 32C, and a connecting pin 32D, but is not limited to this embodiment. For example, the connecting link portion 32 may be composed of a chain or a wire. That is, the chain or wire as the connecting link portion 32 may be pulled and tensioned by the oscillating arm 31, and the chain or wire may be configured to pull and swing the tillage depth adjustment cam 34. In this embodiment, when the pressing force is no longer applied to the receiving member 30B, the chain or wire loosens. Therefore, as in the above-described embodiment, even if the oscillating arm 31 swings, the tillage depth adjustment cam 34 will no longer be linked to the swinging of the oscillating arm 31.

[0098] (5) In the embodiments described above, the locking portion 52 as the "second part" has three recesses (first recess 52a, second recess 52b, and third recess 52c) formed therein. However, in the present invention, there may be two "multiple recesses" or four or more. Alternatively, the locking portion 52 may not have any recesses formed therein, and a flat surface portion may be formed on the locking portion 52, and the contact position between the swinging member 51 and the flat surface portion of the locking portion 52 may be changed.

[0099] (6) In the above-described embodiment, a pair of upper and lower protruding portions are formed on the upper portion of the first recessed portion 52a and the lower portion of the third recessed portion 52c, and the first recessed portion 52a, the second recessed portion 52b, and the third recessed portion 52c are arranged vertically between these pairs of upper and lower protruding portions to form a "common recess," but the embodiment is not limited to this. For example, a "common recess" does not have to be formed, and a pair of upper and lower protruding portions are not formed on the upper portion of the first recessed portion 52a and the lower portion of the third recessed portion 52c, and instead, a configuration in which multiple recesses are simply arranged in a line along the longitudinal direction of the swinging arm 31 is possible. Alternatively, the "common recess" may be formed as a single recess corresponding to the swinging range of the swinging member 51.

[0100] (7) In the above-described embodiment, the receiving member 30B swings back and forth, but the receiving member 30B may also be configured to swing up and down. In this case, the linked swinging arm 31 may extend back and forth along the machine body, and the multiple recesses may be arranged along the longitudinal direction of the linked swinging arm 31.

[0101] (8) In the above-described embodiment, four through holes 31h are formed at the lower end of the oscillating arm 31 and three through holes 35h are formed at the free end of the oscillating part 35, but the embodiment is not limited to this. It is also possible to have a configuration in which one of the through holes 31h and 35h is provided in multiple locations, and the other of the two is provided in only one location. Furthermore, the number of through holes 31h and 35h can be changed as appropriate.

[0102] (9) In the above-described embodiment, when the operator switches the swinging member 51 to three stages, the engagement pin 51a may come into contact with the protrusion between the first recessed portion 52a and the second recessed portion 52b, or the protrusion between the second recessed portion 52b and the third recessed portion 52c, causing the linked swinging arm 31 to swing slightly. Even in such a case, the first link member 32A and the second link member 32B in the connecting link portion 32 are loose enough to swing freely with each other and are not pulled straight. In other words, even if the linked swinging arm 31 swings slightly due to the swinging of the swinging member 51 by the work vehicle, the play in the connecting link portion 32 may prevent it from being linked to the swinging of the linked swinging arm 31. Furthermore, when the operator switches the oscillating member 51 in three stages, the engagement pin 51a may be configured not to come into contact with the protrusion between the first recessed portion 52a and the second recessed portion 52b, or the protrusion between the second recessed portion 52b and the third recessed portion 52c.

[0103] Furthermore, the configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. In addition, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention.

[0104] The present invention can be applied to a tractor equipped with a three-point linkage mechanism for mounting a work device so that it can be raised and lowered.

[0105] 12: Three-point linkage mechanism 15: Working device 30: Load receiving part 31: Linked oscillating arm (linkage mechanism) 31h: Through hole (linkage ratio changing part) 32: Connecting link part (linkage mechanism) 34: Tillage depth adjustment cam (linkage mechanism, sensitivity changing part) 35: Linked oscillating part (linkage mechanism) 35h: Through hole (linkage ratio changing part) 36: Connecting rod (linkage mechanism) 50p: Detent recess (positioning mechanism) 50q: Detent recess (positioning mechanism) 50r: Detent recess (positioning mechanism) 51: Oscillating member (first part) 51o: Ball (positioning mechanism) 51p: Coil spring member (positioning mechanism) 52: Locking part (second part, common recess) 52a: First recess (multiple recesses) 52b: Second recess (multiple recesses) 52c: Third recess (multiple recesses) P: Pivot axis Q1: Pivot axis

Images