Title of Invention	WORK VEHICLE
Abstract	A work vehicle that comprises a drive mechanism whereby a ground" engaging implement coupled with a vehicle body is operated upward and downward relative to the vehicle body,; a working depth detection mechanism; and a link mechanism for coupling the detection mechanism and the drive mechanism, and operating the drive mechanism so that the working depth detected by the working depth detection mechanism is at the set working depth; and is configured such that the link mechanism operates the drive mechanism in a state in which the upward speed at which the ground-engaging implement is raised by a change that causes the working depth detected by the working depth detection mechanism to be greater by a specific amount than the set working depth is greater than the lowering speed at which the ground-engaging implement is lowered by a change that causes the working depth detected by the working depth detection mechanism to be less by a specific amount than the set working depth.

Title of Invention

WORK VEHICLE

Abstract

A work vehicle that comprises a drive mechanism whereby a ground" engaging implement coupled with a vehicle body is operated upward and downward relative to the vehicle body,; a working depth detection mechanism; and a link mechanism for coupling the detection mechanism and the drive mechanism, and operating the drive mechanism so that the working depth detected by the working depth detection mechanism is at the set working depth; and is configured such that the link mechanism operates the drive mechanism in a state in which the upward speed at which the ground-engaging implement is raised by a change that causes the working depth detected by the working depth detection mechanism to be greater by a specific amount than the set working depth is greater than the lowering speed at which the ground-engaging implement is lowered by a change that causes the working depth detected by the working depth detection mechanism to be less by a specific amount than the set working depth.

Full Text	WORK VEHICLE BACKGROUND OF THE INVENTION 1, Field of the Invention The present invention relates to a work vehicle equipped with a vehicle body that is supported by a plurality of wheels; a drive mechanism that raises and lowers, relative to the vehicle body, a ground-engaging implement that is connected to the vehicle body: a working depth detection mechanism provided to the ground-engaging implement to detect the working depth of the ground-engaging implement; and a link mechanism that links the detection mechanism and the drive mechanism and that operates the drive mechanism so that the working depth detected by the working depth detection mechanism reaches a set operation depth. 2, Description of the Related Art In the work vehicle, the raising and lowering of a ground-engaging implement is controlled by the operation of a drive mechanism based on a link mechanism, and the work vehicle can work while maintaining the working depth of the ground-engaging implement at or near the set working depth, regardless of the longitudinal inclination or the like of the vehicle. A conventional example of a work vehicle of the above type is a tractor described in, e.g., JP 2005-176696. The tractor described in the present document is configured such that a rotary tiller is coupled as a ground-engaging implement at the rear of a vehicle body frame via a link mechanism. The tractor is equipped with a hydraulic cylinder as a drive mechanism provided within a transmission case; an interlock mechanism whereby an output arm portion of a tilling depth detection mechanism as a working depth detection mechanism provided to the rotary tiller is interlocked with the main actuator of a control valve of the hydraulic cylinder; and a feedback mechanism for operatively connecting a lift arm of the link mechanism with a feedback actuator of the control valve. The hydraulic cylinder swings the link mechanism upward and downward relative to a vehicle body frame, thereby raising and lowering the rotary tiller relative to the vehicle body. The tilling depth detection mechanism detects the depth of tilling by the rotary tiller, with a rear cover that covers the rear of a tilling rotor as the contact sensor. That is, the tilling depth is detected based on the swing angle of the rear cover relative to an upper cover. The interlock mechanism and the feedback mechanism link the tilling depth detection mechanism and the control valve of the hydraulic cylinder so as to operate the hydraulic cylinder in a state in which the tilling depth detected by the tilling depth detection mechanism reaches the set tilling depth set by using the tilling depth setting lever. In the work vehicle, when the depth of working by the ground-engaging implement is less than the set working depth, operating the actuator of the link mechanism based on the results detected by the working depth detection mechanism causes the drive mechanism to lower the drive ground-engaging implement, and the working depth of the ground-engaging implement to increase. At the above time, the more rapidly the ground-engaging implement is lowered, the more rapidly the working depth of the ground-engaging implement increases, and the rapidly the drive load and the travel of the vehicle tend to increase. Moreover, when the depth of working by the ground-engaging implement is greater than the set working depth, operating the actuator of the link mechanism based on the results detected by the working depth detection mechanism causes the drive mechanism to raise the drive ground-engaging implement, and the working depth of the ground-engaging implement to decrease. At the above time, the more slowly the ground-engaging implement is raised, the longer it takes to decrease the working depth of the ground-engaging implement, and the longer it takes to increase the drive load and the travel of the vehicle due to the increased working depth. SUMMARY OF THE INVENTION An object of the present invention is to provide a work vehicle capable of maintaining the depth of work by a ground engaging implement at or near the set working depth, while making it less likely for the aforementioned travel and work load problems to occur. The work vehicle of the present invention comprises- a vehicle body supported by a plurality of wheels; a drive mechanism for vertically moving a ground-engaging implement coupled with the vehicle body; a working depth detection mechanism provided to the ground-engaging implement to detect the working depth of the ground-engaging implement; and a link mechanism for coupling the detection mechanism and the drive mechanism, and operating the drive mechanism so that the working depth detected by the working depth detection mechanism is at the set working depth; wherein the link mechanism operates the drive mechanism in a state in which the upward speed at which the ground-engaging implement is raised by a change that causes the working depth detected by the working depth detection mechanism to be greater by a specific amount than the set working depth is greater than the lowering speed at which the ground-engaging implement is lowered by a change that causes the working depth detected by the working depth detection mechanism to be less by a specific amount than the set working depth. According to such a configuration, it is possible to control the elevation of the ground-engaging implement so that the depth of working by the ground-engaging implement reaches the set working depth or approximately the same working depth. That is, when the depth of working by the ground-engaging implement becomes greater than the set working depth, the link mechanism operates the actuator on the basis of the working depth detected by the working depth detection mechanism. The drive mechanism is driven upward, and the ground-engaging implement is raised so that the depth of working by the working depth detection mechanism is at the set working depth. On the other hand, when the depth of working by the ground-engaging implement becomes less than the set working depth, the link mechanism operates the actuator on the basis of the working depth detected by the working depth detection mechanism. The drive mechanism is driven downward, and the ground-engaging implement is lowered so that the working depth of the working depth detection mechanism is at the set working depth. When raised, the ground-engaging implement rises more rapidly than when lowered. That is, even if the amount of change in the working depth detected by the working depth detection mechanism when the ground-engaging implement is raised is equal to the amount of change in the working depth detected by the working depth detection mechanism when the ground-engaging implement is lowered, the upward speed produced by the raising of the ground-engaging implement on the basis of the working depth detected by the working depth detection mechanism becomes greater than the downward speed produced by the lowering of the ground-engaging implement on the basis of the working depth detected by the working depth detection mechanism. Compared with the downward case, in the upward case the inertia acts more readily on the ground-engaging implement, and movement of the ground-engaging implement is more likely to speed up. Accordingly, the ground-engaging implement is raised rapidly after the working depth increases, and the drive load and travel of an automotive vehicle, which increase with the working depth, are more likely to decrease rapidly. The ground-engaging implement is lowered slowly after the working depth decreases, and rapid change in the drive load and travel of an automotive vehicle as the result of the lowering of the ground-engaging implement is less likely to occur. As a result, a drop in engine speed caused by controlling the elevation of the ground-engaging implement, and other problems are less likely to occur. Therefore, it is possible to work efficiently and comfortably. In this aspect, a coordination mechanism is linked between the detection mechanism and the actuator provided to the drive mechanism, and the drive mechanism is operated by transmitting a displacement of the detection mechanism via the actuator. In this aspect, the actuator preferably has' an actuator body switchable between a drive state for driving the drive mechanism and a neutral state for stopping the operation of the drive mechanism; a drive operating element for switching the actuator body to the drive state; and a neutral operating element for switching the actuator body to the neutral state; and the link mechanism preferably has: a drive interlock mechanism for operatively connecting the working depth detection mechanism with the drive operating element; a neutral interlock mechanism for operatively connecting the drive mechanism with the neutral operating element; and an operating element interlock mechanism for operatively connecting the drive operating element and the neutral operating element so as interlock the neutral interlock mechanism with the neutral operating element and to operate the drive operating element when the ground-engaging implement is raised. According to such an aspect, when the depth of working of the ground-engaging implement increases or decreases beyond the set working depth, the drive interlock mechanism switches the actuator body to the drive state on the basis of the working depth detected by the working depth detection mechanism. As the ground-engaging implement ascends or descends, the neutral interlock mechanism thereby returns the actuator body to the neutral state on the basis of the actuation of the drive mechanism, and the ground-engaging implement reaches the coupling height at which the working depth is at the set working depth. The ground-engaging implement is thereby made more likely to rise rapidly. That is, when, as the ground-engaging implement is raised, the neutral interlock mechanism operates the neutral operating element and returns the actuator body to the neutral state, the neutral interlock mechanism is caused to interlock with the neutral operating element, the operating element interlock mechanism is operated, and the operating element interlock mechanism operates the drive operating element. Then, when the neutral interlock mechanism attempts to return the actuator body to the neutral state while the ground-engaging implement is raised, the drive operating element can be operated upward by using the operating element interlock mechanism. The upward speed at which the ground-engaging implement is raised by changing the unit change amount to a greater working depth detected by the working depth detection mechanism can thereby be made higher than the downward speed at which the ground-engaging implement is lowered by changing the unit change amount to a lesser working depth detected by the working depth detection mechanism, and the drive mechanism can be operated. In this aspect, the operating element interlock mechanism preferably has a link having a slot and a catch that is operatively connected with the neutral operating element and engages the slot; and the operating element interlock mechanism is preferably configured so that the driving force from the drive mechanism is transmitted to the drive operating element via the operating element interlock mechanism by bringing the catch into contact with one end of the slot when the ground-engaging implement is raised. In this aspect, the operating element interlock mechanism is configured such that transmission of the driving force from the drive mechanism to the drive operating element via the operating element interlock mechanism is canceled by releasing the contact between the catch and one end of the slot when the ground-engaging implement is lowered. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of the rear of a work vehicle; FIG. 2 is a side view of a link mechanism; FIG. 3 is a top view of the link mechanism; FIG. 4 is a rear view of an actuator; FIG. 5 is a hydraulic circuit diagram of a hydraulic cylinder; FIG. 6 is a view showing the state of operation of the actuator and the action status of the link mechanism in a state in which the depth of tilling by a tiller is the set tilhng depth; FIG. 7 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is changed to a level less than the set tilling depth; FIG. 8 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is returned to the set tilling depth by lowering the tiller; FIG. 9 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is changed to a level greater than the set tilling depth; and FIG. 10 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is returned to the set tilling depth by raising the tiller. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of the rear of a work vehicle of an embodiment of the present invention. The work vehicle according to the embodiment of the present invention comprises a vehicle having a left-and-right pair of front wheels (not shown), a left-and-right pair of drivable rear wheels 1, 1, and a steering unit equipped with a driver seat 2 provided at the rear of the vehicle body. The vehicle is also provided with a link mechanism 10 disposed at the rear of a vehicle body frame 3 of the vehicle. In the work vehicle according to the embodiment of the present invention, a rotary tiller 20 (below abbreviated as "tiller 20") is coupled via the link mechanism 10 to the rear of the vehicle body, thereby forming a riding-type tiller. Specifically, as shown in FIG. 1, the link mechanism 10 comprises a left-and-right pair of lift arms 11, 11 provided so as to swing vertically at the upper portion of a transmission case 4 that forms the rear of the vehicle body frame 3; a left-and-right pair of lower links 12, 12 that extend so as to swing vertically toward the rear of the vehicle body from the lower portion of the transmission case 4; a top link 14 that extends so as to swing vertically toward the rear of the vehicle body from a top link bracket 13 provided at the rear of the transmission case 4; and a lift rod 15 that couples the lift arm 11 and the lower link 12 on the left and right sides of the link mechanism 10. The extending ends of the left-and-right pair of lower links 12, 12 and the top Link 14 are coupled to a coupling frame 21 provided to the tiller 20. The left-and-right pair of lift arms 11, 11 are interlocked with a hydraulic cylinder 5 (see FIGS, 4 and 5) located within the transmission case 4, via a rotary pivot 16 that couples the left-and-right pair of lift arms 11, 11 to the transmission case 4. That is, the left-and-right pair of lift arms 11, 11 are swung vertically by the rotary operation of the pivot 16 actuated by the hydraulic cylinder 5, whereby the link mechanism 10 is swung vertically related to the vehicle body frame 3 and whereby the tiller 20 is operated vertically between a lowered state in which a tilling rotor 22 of the tiller contacts the ground, and in a raised state in which the tilling rotor 22 is raised from the soil surface; and the tiller 20 in the lowered state is operated vertically relative to the vehicle body frame 3. The hydraulic cylinder 5 can thereby vertically adjust the tiller 20 relative to the work vehicle, vary the depth of tilling (referred to hereinbelow as "tilling depth") by the tilling rotor 22 of the tiller 20, and maintain constant the depth of tilling by the tiller 20 regardless of the longitudinal inclination and elevation of the work vehicle relative to the soil surface travelled. The work vehicle is equipped with a motive power take-off shaft 6 rotatably provided to the rear of the transmission case 4, and the driving force output by the engine (not shown) provided to the front portion of the vehicle body is transmitted from the motive power take-off shaft 6 to the tiller 20 via a rotary transmission shaft 7 that is coupled with the motive power take-off shaft 6. As shown in FIG. 4, the work vehicle is equipped with an operating portion 30 provided to the transmission case 4 in order to operate the hydraulic cylinder 5. As shown in FIGS. 1, 2, and 6, the work vehicle is equipped with a tilling depth setting lever 8 located beside the driver seat 2, and a link mechanism S whereby a drive operating element 31 and a neutral operating element 32 (see FIG. 4) of the operating portion 30 are linked to a tilling depth detection mechanism 50 provided to the tiller 20. The elevation of the tiller 20 in the work vehicle is thereby controlled so that the tilling depth of the tiller 20 reaches the tilhng depth set by the tilling depth setting lever 8 or a tilling depth close thereto even in the event that the vehicle body longitudinally inchnes or rises and falls relative to the travel soil surface after a front wheel (not shown) or a rear wheel 1 enters a depressed portion of the travelled soil surface or drives over an elevated portion of the travelled soil surface. FIG. 4 is a rear view of the operating portion 30. FIG. 5 is a hydraulic circuit diagram for operating the hydraulic cylinder 5. As shown in the drawings, the operating portion 30 is configured with a drive operating element 31 and a neutral operating element 32, as well as an actuator body 33 that is provided within the transmission case 4, and a balance link 35 that links a spool operation shaft 34 of the actuator body 33 to the drive operating element 31 and the neutral operating element 32. As shown in FIGS. 4 and 5, the actuator body 33 is equipped with a valve case 36 that is connected to the transmission case 4, as well as a main spool 37, a lowering valve 38, a relief valve 39, and an unload valve 40, which are disposed in the valve case 36. The main spool 37 is coupled with the spool operation shaft 34. An operation shaft 38a of the lowering valve 38 engages a tie rod 41 connected to the spool operation shaft 34. The central portion of the balance link 35 is rotatably coupled with an operation arm portion 34a of the spool operation shaft 34. The drive operating element 31 is configured with a rotary support shaft portion 31a and a swing arm portion 31b supported so as to rotate integrally with the rotary support shaft portion 31a; and is rotatably supported by the rotary support shaft portion 31a in a side wall portion 4a of the transmission case 4. A swing arm portion 31b engages one side of the balance link 35. The neutral operating element 32 is configured with a rotary support shaft portion 32a and a swing arm portion 32b that is supported so as to be able to integrally rotate with the rotary support shaft portion 32a; and is rotatably supported by the rotary support shaft portion 32a in the side wall portion 4a. The swing arm portion 32b engages the other end of the balance link 35. FIG. 5 shows a state in which a coupling pin 42 that couples the balance link 35 and the arm portion 34a is in the neutral position. When the coupling pin 42 is in the neutral position, the main spool 37 discharges the pilot hydraulic pressure from the unload valve 40, and a tie rod 41 brings the lowering valve 38 into a closed state. The unload valve 40 then returns to the tank the hydraulic pressure from a hydraulic pump 43, and the lowering valve 38 stops the discharge of the hydraulic cylinder 5. That is, the actuator body 33 transitions to the neutral state so as to stop the hydraulic cylinder 5. When the drive operating element 31 swings upward (U) around the axial center of the rotary support shaft portion 31a while the actuator body 33 is in the neutral state, the swing arm portion 31b of the drive operating element 31 swings about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32. Then the coupling pin 42 moves from the neutral position to the valve case 36 side, and the spool operation shaft 34 is slid upward (U) against the resistance of the downward-urging spring 44, and switches the main spool 37. The tie rod 41 then moves relative to the operation shaft 38a of the lowering valve 38 and maintains the lowering valve 38 in the closed state. The main spool 37 then supplies the pressurized oil from the hydraulic pump 43 to the hydraulic cylinder 5. The actuator body 33 transitions to the upward drive state so as to drive the hydraulic cylinder 5 to the side on which the lift arm 11 rises. When the neutral operating element 32 then swings in rotational direction (A) around the axial center of the rotary support shaft portion 32a, the swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing arm portion 31a of the drive operating element 31, and moves to the side on which the coupling pin 42 of the balance link 35 is separated from the valve case 36. The appropriate amount of operation of the neutral operating element 32 causes the coupling pin 42 to return to the neutral position, and causes the actuator body 33 to return to the neutral state. When the drive operating element 31 is swung downward (D) around the axial center of the rotary support shaft portion 31a from the state in which the actuator body 33 is in the neutral state, the swing arm portion 31b of the drive operating element 31 is swung about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32. The coupling pin 42 of the balance link 35 then moves from the neutral position to the side opposite the valve case 36. The spool operation shaft 34 is slid downward (D) by a downward-urging spring 44, and the main spool 37 is switched. At the above time, the tie rod 41 pulls the operation shaft 38a of the lowering valve 38, and the lowering valve 38 transitions to the open state. The unload valve 40 then returns to the tank the hydraulic pressure from the hydraulic pump 43, and the lowering valve 38 discharges the pressurized oil of the hydraulic cylinder 5. That is, the actuator body 33 transitions to the lowering-side drive state so as to drive the hydraulic cylinder 5 to the side on which the lift arm 11 moves down. The downward-urging spring 44 is switches/urges the actuator body 33 to the lowering-side drive state. At this time, when the neutral operating element 32 swings in rotational direction (B) around the axial center of the rotary support shaft portion 32a, the swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing arm portion 31b of the drive operating element 31, and the coupling pin 42 of the balance link 35 moves toward the valve case 36. When the amount of operation of the neutral operating element 32 is appropriate, the coupling pin 42 of the balance link 35 returns to the neutral position, and the actuator body 33 returns to the neutral state. As shown in FIG. 1, the tilling depth detection mechanism 50 has a rotor rear cover. That is, as shown in FIGS. 1 and 6, the rotor rear cover 50 is supported at a rotor top cover 51 by a coupling pin 52 in a configuration in which the rear of the tilling rotor 22 is covered. The rotor top cover 51 is fastened to a frame 23 of the tiller 20. The coupling pin 52 rotatably couples the upper portion of the rotor rear cover 50 to the rear end portion of the rotor top cover 51. The upper end of a spring support rod 53, whose lower end is coupled to the free end of the rotor rear cover 50, is supported to as to be able to slide vertically at a bracket 54 of a support arm 24 that extends from the frame 23. A cover-lowering spring 55 mounted on the spring support rod 53 downwardly urges the spring support rod 53, with the bracket 54 as the reaction force member. That is, the rotor rear cover 50 is supported so as to swing upward and downward relative to the frame 23 of the tiller 20 and around an axial center P of the coupling pin 52, which is transverse to the vehicle, and is downwardly urged by the cover-lowering spring 55 so as to contact the surface of the soil tilled by the tilling rotor 22. A change in the tilling depth of the tiller 20 thereby causes the rotor rear cover 50 to swing up and down relative to the rotor top cover 51 and around the axial center P, and the swing angle of the rotor rear cover 50 to change relative to the rotor top cover 51. That is, the rotor rear cover 50 detects the swing angle relative to the rotor top cover 51 as the tilling depth. FIG. 2 is a side view of the link mechanism S, and FIG. 3 is a top view of the link mechanism S. As shown in the drawings, the link mechanisms S is configured with a drive interlock mechanism 60 having a drive operation arm 61 provided so as to be able to rotate integrally with the rotary support shaft portion 31a of the drive operating element 31, a neutral interlock mechanism 70 having a neutral operation arm 71 provided so as to be able to rotate integrally with the rotary support shaft portion 32a of the neutral operating element 32, and a operating element interlock mechanism 80 having an output link 81 provided so as to be able to rotate integrally with the rotary support shaft portion 32a of the neutral operating element 32. As shown in FIGS. 2 and 3, the drive interlock mechanism 60 is configured so as to have, in addition to a drive operation arm 61, a valve-side link 62 whose one end is coupled to the drive operation arm 61 via a coupling pin 61a; a sensor-side link 63 that is interlocked to the other end of the valve-side link 62 via an interlock pin 63a; a tie rod 64 that couples the front-side end of the vehicle body to one end of the sensor-side link 63 via a coupling pin 63b; a rod-side relay link 65 that is coupled to the end at the rear of the vehicle body of the tie rod 64 via a coupling 65a; a cable-side relay link 66 provided so as to be able to rotate integrally with the rotary pivot 65b of the rod-side relay link 65; and a sensor coupling cable 67 that couples the work vehicle-side end of an inner cable 67a to the cable-side relay link 66. As shown in FIG. 6, the tiller-side end of the inner cable 67a of the sensor coupling cable 67 is coupled to a cable-side arm 68a of a relay 68 provided with the rotor top cover 51. The relay 68 can swing around the axial center of a coupling pin 69a on a bracket 69 provided to the rotor top cover 51. The above relay 68 is equipped with, in addition to the cable-side arm 68a, a sensor-side arm 68b that is coupled so as to be able to swing integrally with the cable-side arm 68a, and a tie rod 68c for operatively connecting the sensor-side arm 68b to the rotor rear cover 50, In the above manner, the sensor coupling cable 67 is interlocked with the rotor rear cover 50 so that the swing of the rotor rear cover 50 is transmitted as detection information to the cable-side relay link 66. The rotary pivot 65b of the rod-side relay link 65 is rotatably supported by the top link bracket 13, The rod-side relay link 65 and the cable-side relay link 66 are swingably urged by a return spring RB supported on the rotary pivot 65b. The link is urged in the direction that pulls the sensor coupling cable 67 and pushes the tie rod 64. As shown in FIGS. 2 and 3, the valve-side link 62 has a slot 62a provided to the side that is interlocked with the sensor-side link 63. The interlock pin 63a for operatively connecting the valve-side link 62 and the sensor-side link 63 is supported on the sensor-side link 63 so as to be slidably and rotatably inserted into the slot 62a. The end located on the side opposite from the side where the interlock pin 63a of the sensor-side link 63 is located is coupled to a support link 82 by a coupling pin 82a. As shown in FIGS. 2 and 3, a cylindrical-shaft-shaped rotary pivot 82b of the support link 82 is rotatably supported by the tilling depth setting lever 8 via a pivot 8a; and the sensor-side link 63 is supported by the tilling depth setting lever 8 via the support link 82 and the pivot 8a. As shown in FIGS. 2 and 3, the neutral interlock mechanism 70 is configured so as to have, in addition to the neutral operation arm 71, a tie rod 72 that rotatably couples the end of the front side of the vehicle body to the neutral operation arm 71, and a rod support rod 74 that uses a pair of positioning screws 73, 73 to couple the end portion of the tie rod 72 to the rear side of the vehicle body. The base of the rod support rod 74 is supported at a location biased in relation to the swing axial center of the lift arm 11 at the base of the lift arm 11. As a result, the rod support rod 74 interlocks the tie rod 72 to the hydraulic cylinder 5 via the lift arm 11. As shown in FIGS. 2 and 3, the operating element interlock mechanism 80 is configured with the output link 81, as well as a tie rod 83 one end of which is rotatably coupled to the output link 81, a relay link 84 to which the other end of the tie rod 83 is rotatably coupled, the support link 82, the sensor-side link 63, the valve-side link 62, and the drive operation arm 61. As shown in FIG, 4, the output link 81 is coupled so as to be able to rotate integrally with the cylindrical-shaft-shaped rotary pivot 71a of the neutral operation arm 71, and is thereby coupled so as to be able to rotate integrally with the rotary support shaft portion 32a of the neutral operating element 32. As shown in FIG. 3, the relay link 84 is coupled so as to be able to rotate integrally with the pivot portion 82b of the support link 82, The relay link 84 is thereby supported by the tilling depth setting lever 8 via the rotary pivot 82b and the pivot 8a, and swings integrally with the support link 82. That is, the drive interlock mechanism 60 interlocks the rotor rear cover 50 and the drive operating element 31 so that, as the depth of tilling detected by the rotor rear cover 50 becomes greater or less than the tilling depth set by using the tilling depth setting lever 8, the actuator body 33 of the operating portion 30 is switched to an upward or downward drive state that corresponds to the change in the detected tilling depth. The neutral interlock mechanism 70 interlocks the hydraulic cylinder 5 and the neutral operating element 32 so that, as the hydraulic cylinder 5 raises or lowers the tiller 20 to the coupling height at which the resulting tilling depth reaches the set tilling depth, the actuator body 33 of the operating portion 30 is returned to the neutral state. The operating element interlock mechanism 80 interlocks the drive operating element 31 and the neutral operating element 32 so that the upward displacement amount and the upward speed at which the tiller 20 is raised by a change in the unit change amount at which the tilling depth detected by the rotor rear cover 50 increases are greater than the downward displacement amount and the downward speed at which the tiller 20 is lowered by a change in the unit change amount at which the tilling depth detected by the rotor rear cover 50 decreases. Fig. 6 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism s, which is in a state in which the depth of tilling by the tiller 20 is the set tilling depth; As shown in the drawing, when the tiller 20 is at the set tilling depth, the swing angle between the rotor rear cover 50 and the rotor top cover 51 is the reference swing angle that corresponds to the set tilling depth. Based on the tilling depth detected by the rotor top cover 51, the drive interlock mechanism 60 operates the drive operating element 31 of the operating portion 30 at the standard orientation that corresponds to the set tilling depth. Based on the swing state of the lift arm 11 as the state of operation of the hydraulic cylinder 5, the neutral interlock mechanism 70 operates the neutral operating element 32 of the operating portion 30 in the neutral orientation. The coupling pin 42 of the balance link 35 is then brought to the neutral position by the operation of the balance link 35 based on the drive operating element 31 and the neutral operating element 32. The actuator body 33 is thereby brought to the neutral state, and the hydraulic cylinder 5 is stopped. FIG, 7 is an illustration of the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 was changed to a level less than the set tilling depth. As the depth of tilling by the tiller 20 changes to a depth less than the set tilhng depth, the rotor rear cover 50 moves down relative to the rotor top cover 51. As a result, when the depth of tilling by the tiller 20 changes to a depth less than the set tilling depth, as shown in FIG. 7, the drive interlock mechanism 60 swings the sensor-side link 63 to the front side of the vehicle body and around the axial center of the coupling pin 82a by pushing the tie rod 64 based on the downward swinging the rotor rear cover 50, moves the interlock pin 63a of the sensor-side link 63 toward the vehicle body front of the slot 62a of the valve-side link 62, allows the drive operation arm 61 to be swung by the downward urging force of the operating portion 30, and moves the drive operating element 31 of the operating portion 30 downward from the standard orientation by using the downward urging force of the operating portion 30. At this time, the hydraulic cylinder 5 is still stopped, whereby the neutral operation arm 71 of the neutral interlock mechanism 70 brings the neutral operating element 32 of the operating portion 30 to the neutral orientation. The swing arm portion 31b of the drive operating element 31 swings about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32; the coupling pin 42 of the balance link 35 moves from the neutral position to the side (i.e., down side D) away from the valve case 36; and the actuator body 33 of the operating portion 30 switches to the downward-side drive state. As a result, the hydraulic cylinder 5 is driven to the downward side, and the tiller 20 is lowered. FIG. 8 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 is returned to the set tilling depth by lowering the tiller 20. When the depth of tilling by the tiller 20 returns to the set tilling depth as the tiller 20 is lowered, the lift arm 11 descends more than at the start of the lowering operation. When the depth of tilhng by the tiller 20 returns to the set tilling depth, as shown in FIG. 8, the neutral interlock mechanism 70 thereby swings the neutral operation arm 71 by pushing the tie rod 72 based on the lowering force of the lift arm 11 as the hydraulic cylinder 5 actuating force, and actuating the neutral operating element 32 of the operating portion 30 from the standard orientation. The swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing arm portion 31b of the drive operating element 31; the coupling pin 42 of the balance link 35 moves toward the valve case 36 and returns to the neutral position; and the actuator body 33 of the operating portion 30 returns to the neutral state. The hydraulic cylinder 5 is thereby stopped and the tiller 20 is set to the coupling height at which the tilling depth is equal to the set tilling depth. FIG. 9 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 was changed to a level greater than the set tilling depth. As the depth of tilling by the tiller 20 changes to a deeper level than the set tilling depth, the rotor rear cover 50 rises relative to the rotor top cover 51. When the depth of tilling by the tiller 20 changes to a level greater than the set tilling depth, as shown in FIG. 9, the drive interlock mechanism 60 thereby swings the sensor-side link 63 toward the vehicle body rear and around the axial center of the coupling pin 82a by pulling the tie rod 64 based on the upward swing of the rotor rear cover 50; pressure is created toward the valve-side link 62 by the interlock pin 63a of the sensor-side link 63; the drive operation arm 61 is swung by the valve-side link 62; and the drive operating element 31 of the operating portion 30 is brought from the standard orientation to the upward side. At this time, the hydraulic cylinder 5 is stilled stopped, whereby the neutral operation arm 71 of the neutral interlock mechanism 70 brings the neutral operating element 32 of the operating portion 30 to the neutral orientation. The swing arm portion 31b of the drive operating element 31 then swings about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32; the coupling pin 42 of the balance link 35 moves from the neutral position toward the valve case 36 (i.e., the upward U); and the actuator body 33 of the operating portion 30 switches to the upward drive state. The hydraulic cylinder 5 is thereby driven upward and the tiller 20 is raised, FIG. 10 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 is returned to the set tilling depth by raising the tiller 20. When the depth of tilling by the tiller 20 returns to the set tilling depth in conjunction with the raising of the tiller 20, the hft arm 11 is higher than at the start of the raising operation. When the depth of tilling by the tiller 20 returns to the set tilling depth, as shown in FIG. 10, the neutral interlock mechanism 70 thereby swings the neutral operation arm 71 by pulling the tie rod 72 based on the upward force of the lift arm 11 as the hydraulic cylinder 5 actuating force; and actuates the neutral operating element 32 of the operating portion 30 from the standard orientation. The swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing operation arm portion 31b of the drive operating element 31; the coupling pin 42 of the balance link 35 moves to the side away from the valve case 36 and returns to the neutral position; and the actuator body 33 of the operating portion 30 returns to the neutral state. The hydraulic cylinder 5 is thereby stopped and the tiller 20 is brought to the coupling height at which the tilling depth is equal to the set tilling depth. As shown in FIGS. 7 and 8, when the lift arm 11 descends, the operating element interlock mechanism 80 does not operate the drive operating element 31 regardless of the actuation by the neutral interlock mechanism 70. That is, during descent of the lift arm 11, the output link 81 interlocked with the neutral operating element 32 swings to the left side in the drawing around the axial center of the rotary support shaft portion 32a, and the driving force of the output link 81 is transmitted to the support link 82 via the tie rod 83 and the relay link 84. The support link 82 then swings to the right in the drawing around the axial center of the pivot 8a; the sensor-side link 63 swings to the right in the drawing around the axial center of the coupling pin 63b; and the interlock pin 63a is operated to the side away from the left end of the slot 62a in the drawing. When the lift arm 11 is lowered, the operating element interlock mechanism 80 thereby blocks the interlocking of the neutral operating element 32 and the drive operating element 31, and the application of the urging force to the drive operating element 31 is terminated. When the swing angle of the rotor rear cover 50 is brought to the dead zone as the reference swing angle in conjunction with the lowering of the lift arm 11, the sensor-side link 63 is swung around the axial center of the coupling pin 82a by the tie rod 64 as a result of the rising of the rotor rear cover 50 relative to the rotor top cover 51, whereby the interlock pin 63a is positioned at the end of the slot 62a on the left side of the drawing, and the valve-side link 62 supports the drive operation arm 61, with the interlock pin 63a serving as the reaction force member. The neutral operation arm 71 of the neutral interlock mechanism 70 operates the neutral operating element 32. When the depth of tilling by the tiller 20 returns to the set tilling depth, the operation of the balance, link 35 by the drive operating element 31 and the neutral operating element 32 thereby allows the coupling pin 42 of the balance link 35 to be brought to the neutral position, the actuator body 33 of the operating portion 30 to be brought to the neutral state; and the hydraulic cylinder 5 to be stopped. By contrast, as shown in FIGS. 9 and 10, when the lift arm 11 is raised, operation by the neutral interlock mechanism 70 causes the operating element interlock mechanism 80 to operate the drive operating element 31 in opposition to the downward swing of the rotor rear cover 50 relative to the rotor top cover 51. That is, when the lift arm 11 is raised, the output link 81 interlocked with the neutral operating element 32 swings to the lower-right side of the drawing around the axial center of the rotary support shaft portion 32a, and the driving force of the output link 81 is transmitted to the support link 82 via the tie rod 83 and the relay link 84. The support link 82 swings to the left side in the drawing around the axial center of the pivot 8a; the sensor-side link 63 swings to the left side in the drawing around the axial center of the coupling pin 63b; and the interlock pin 63a contacts the left end of the slot 62a in the drawing. When the lift arm 11 is raised, the operating element interlock mechanism 80 thereby interlocks the neutral operating element 32 and drive operating element 31, and the drive operating element 31 is operated to the upward side in opposition to the lowering of the rotor rear cover 50 relative to the rotor top cover 51. When the swing angle of the rotor rear cover 50 is located in the dead zone as the reference swing angle during the raising of the lift arm 11, there is balance between the operation of the neutral operating element 32 by neutral interlock mechanism 70 and the operation of the drive operating element 31 by the operating element interlock mechanism 80. Therefore, the coupling pin 42 of the balance link 35 returns to the neutral position, the actuator body 33 of the operating portion 30 transitions to the neutral state, and the hydraulic cylinder 5 stops. That is, when the neutral interlock mechanism 70 operates the neutral operating element 32 and returns the actuator body 33 to the neutral state in conjunction with the lowering of the lift arm 11, the neutral interlock mechanism 70 operates the output link 81 of the operating element interlock mechanism 80 by interlocking with the neutral operating element 32. At this time, the valve-side link 62 is not pushed by the interlock pin 63a due to the swing direction of the output link 81, and an operating element interlock mechanism 80 does not operate the drive operating element 32 toward the downward side. By contrast, when the neutral interlock mechanism 70 operates the neutral operating element 32 and returns the actuator body 33 to the neutral state in conjunction with the raising of the lift arm 11, the neutral interlock mechanism 70 operates the output link 81 of the operating element interlock mechanism 80 by interlocking with the neutral operating element 32. At this time, the valve-side link 62 is pressed by the interlock pin 63a due to the swing direction of the output link 81, and the operating element interlock mechanism 80 brings the drive operating element 31 to the upward side. A comparison can thereby made between the upward displacement amount and the upward speed at which the tiller 20 is raised by a change in the unit change amount to a greater tilling depth detected by the rotor rear cover 50, and the downward displacement amount and the downward speed at which the tiller 20 are lowered by a change in the unit change amount to a lesser tilling depth detected by the rotor rear cover 50. When the comparison is made, the link mechanism S operates the hydraulic cylinder 5 in a state in which the upward displacement amount and the upward speed exceed the downward displacement amount and the downward speed, and which is brought about by the action of the operating element interlock mechanism 80; and controls the ascent and descent of the tiller 20 so that the tiller 20 is moved more rapidly by inertial during ascent than during descent. As shown in FIGS. 2 and 3, the base of the tilling depth setting lever 8 is rotatably coupled with the transmission case 4 via the coupling shaft 4b, and the tilling depth setting lever 8 is supported so as to swing longitudinally relative to the vehicle body around the axial center of the coupling shaft 4b. When the tilling depth setting lever 8 is swung in the above manner, the support link 82 swings the sensor-side link 63 around the axial center of the coupling pin 63a, The interlock pin 63b is then brought to the left end of the slot 62a in the drawing and is caused to press on the valve-side link 62; and either the drive operating element 31 is operated by swinging the drive operation arm 61 via the valve-side link 62, or the interlock pin 63b moves to the right of the slot 62a in the drawing and allows the drive operation arm 61 to be swung by the urging force of the spring 44 of the actuator body 33, and the drive operating element 31 is swung by the urging force of the spring 44 of the actuator body 33. The movement of the neutral position of the coupling pin 42 of the balance link 35 is then adjusted, and a positioning mechanism (not shown) for creating fuctional resistance that acts on the base of the tilling depth setting lever 8 maintains the tilling depth setting lever 8 in the operating position and maintains the neutral position of the coupling pin 42 of the balance link 35 at the movement-adjustment position. The tilling depth setting lever 8 thereby varies and sets a shallower or deeper level for the tilling depth maintained by controlling the raising and lowering of the tiller 20 with the aid of the link mechanism S. [Other Embodiments] The object of the present invention can be achieved when various implements (e.g., a plow) are coupled in place of the tiller 20. The object of the present invention also is achievable by adopting a configuration in which the tiller 20 is operated upward and downward by using a motor in place of the hydraulic cylinder 5. The object of the present invention also is achievable by adopting a configuration in which the tilling depth is detected by a detection mechanism dedicated to detecting the tilling depth, in place of the rotor rear cover 50. Accordingly, the tiller 20 and the hke are collectively referred to as the ground-engaging implement 20, the hydraulic cylinder 5 and the like are referred to as the drive mechanism 5, and the rotor rear cover 50 and the like are collectively referred to as the tilling depth detection mechanism 50. I/We claim 1. A work vehicle, comprising: a vehicle body supported by a plurality of wheels: a drive mechanism for vertically moving a ground-engaging implement coupled with the vehicle body; a working depth detection mechanism provided to the ground-engaging implement to detect a working depth of the ground-engaging implement; and a link mechanism for coupling the detection mechanism and the drive mechanism, and operating the drive mechanism so that the working depth detected by the working depth detection mechanism is at the set working depth; characterized in that the link mechanism operates the drive mechanism such that an upward speed at which the ground-engaging implement is raised in response to a predetermined amount of increase in the working depth, from a set working depth, detected by the working depth detection mechanism is greater than a lowering speed at which the ground-engaging implement is lowered in response to a predetermined amount of decrease in the working depth, from a set working depth, detected by the working depth detection mechanism. 2. The work vehicle of Claim 1, wherein the link mechanism is linked between the detection mechanism and an operating portion provided to the drive mechanism; and the drive mechanism is operated by transmitting a displacement of the detection mechanism via the operating portion. 3. The work vehicle of Claim 2, the operating portion having: an operating portion body switchable between a drive state for driving the drive mechanism and a neutral state for stopping the operation of the drive mechanism; a drive operating element for switching the actuator body to the drive state; and a neutral operating element for switching the actuator body to the neutral state; and the link mechanism having: a drive interlock mechanism for operatively connecting the working depth detection mechanism with the drive operating element; a neutral interlock mechanism for operatively connecting the drive mechanism with the neutral operating element; and an operating element interlock mechanism for operatively connecting the drive operating element and the neutral operating element so as to operatively connect the neutral interlock mechanism with the neutral operating element and to operate the drive operating element when the ground-engaging implement is raised. 4. The work vehicle of Claim 3, wherein the operating element interlock mechanism has a link having a slot and a catch that is operatively connected with the neutral operating element and engages the slot; and the operating element interlock mechanism is configured such that the driving force from the drive mechanism is transmitted to the drive operating element via the operating element interlock mechanism by bringing the catch into contact with one end of the slot when the ground-engaging implement is raised. 5. The work vehicle of Claim 4, wherein the operating element interlock mechanism is configured such that transmission of the driving force from the drive mechanism to the drive operating element via the operating element interlock mechanism is canceled by releasing the contact between the catch and one end of the slot when the ground-engaging implement is lowered.

Full Text

WORK VEHICLE
BACKGROUND OF THE INVENTION
1, Field of the Invention
The present invention relates to a work vehicle equipped with a vehicle body that is supported by a plurality of wheels; a drive mechanism that raises and lowers, relative to the vehicle body, a ground-engaging implement that is connected to the vehicle body: a working depth detection mechanism provided to the ground-engaging implement to detect the working depth of the ground-engaging implement; and a link mechanism that links the detection mechanism and the drive mechanism and that operates the drive mechanism so that the working depth detected by the working depth detection mechanism reaches a set operation depth.
2, Description of the Related Art
In the work vehicle, the raising and lowering of a ground-engaging implement is controlled by the operation of a drive mechanism based on a link mechanism, and the work vehicle can work while maintaining the working depth of the ground-engaging implement at or near the set working depth, regardless of the longitudinal inclination or the like of the vehicle.
A conventional example of a work vehicle of the above type is a tractor described in, e.g., JP 2005-176696.
The tractor described in the present document is configured such that a rotary tiller is coupled as a ground-engaging implement at the rear of a vehicle body frame via a link mechanism. The tractor is equipped with a hydraulic cylinder as a drive mechanism provided within a transmission case; an interlock mechanism whereby an output arm portion of a tilling depth detection mechanism as a working depth detection mechanism provided to the rotary tiller is interlocked with the main actuator of a control valve of the hydraulic cylinder; and a feedback mechanism for operatively connecting a lift arm of the link mechanism with a feedback actuator of the control valve.
The hydraulic cylinder swings the link mechanism upward and downward relative to a vehicle body frame, thereby raising and lowering the rotary tiller relative to the vehicle body.
The tilling depth detection mechanism detects the depth of tilling by the rotary tiller, with a rear cover that covers the rear of a tilling rotor as the contact sensor. That is, the tilling depth is detected based on the swing angle of the rear cover relative to an upper cover.

The interlock mechanism and the feedback mechanism link the tilling depth detection mechanism and the control valve of the hydraulic cylinder so as to operate the hydraulic cylinder in a state in which the tilling depth detected by the tilling depth detection mechanism reaches the set tilling depth set by using the tilling depth setting lever.
In the work vehicle, when the depth of working by the ground-engaging implement is less than the set working depth, operating the actuator of the link mechanism based on the results detected by the working depth detection mechanism causes the drive mechanism to lower the drive ground-engaging implement, and the working depth of the ground-engaging implement to increase. At the above time, the more rapidly the ground-engaging implement is lowered, the more rapidly the working depth of the ground-engaging implement increases, and the rapidly the drive load and the travel of the vehicle tend to increase.
Moreover, when the depth of working by the ground-engaging implement is greater than the set working depth, operating the actuator of the link mechanism based on the results detected by the working depth detection mechanism causes the drive mechanism to raise the drive ground-engaging implement, and the working depth of the ground-engaging implement to decrease. At the above time, the more slowly the ground-engaging implement is raised, the longer it takes to decrease the working depth of the ground-engaging implement, and the longer it takes to increase the drive load and the travel of the vehicle due to the increased working depth.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a work vehicle capable of maintaining the depth of work by a ground engaging implement at or near the set working depth, while making it less likely for the aforementioned travel and work load problems to occur.
The work vehicle of the present invention comprises-
a vehicle body supported by a plurality of wheels;
a drive mechanism for vertically moving a ground-engaging implement coupled with the vehicle body;
a working depth detection mechanism provided to the ground-engaging implement to detect the working depth of the ground-engaging implement; and

a link mechanism for coupling the detection mechanism and the drive mechanism, and operating the drive mechanism so that the working depth detected by the working depth detection mechanism is at the set working depth;
wherein the link mechanism operates the drive mechanism in a state in which the upward speed at which the ground-engaging implement is raised by a change that causes the working depth detected by the working depth detection mechanism to be greater by a specific amount than the set working depth is greater than the lowering speed at which the ground-engaging implement is lowered by a change that causes the working depth detected by the working depth detection mechanism to be less by a specific amount than the set working depth.
According to such a configuration, it is possible to control the elevation of the ground-engaging implement so that the depth of working by the ground-engaging implement reaches the set working depth or approximately the same working depth.
That is, when the depth of working by the ground-engaging implement becomes greater than the set working depth, the link mechanism operates the actuator on the basis of the working depth detected by the working depth detection mechanism. The drive mechanism is driven upward, and the ground-engaging implement is raised so that the depth of working by the working depth detection mechanism is at the set working depth.
On the other hand, when the depth of working by the ground-engaging implement becomes less than the set working depth, the link mechanism operates the actuator on the basis of the working depth detected by the working depth detection mechanism. The drive mechanism is driven downward, and the ground-engaging implement is lowered so that the working depth of the working depth detection mechanism is at the set working depth.
When raised, the ground-engaging implement rises more rapidly than when lowered.
That is, even if the amount of change in the working depth detected by the working depth detection mechanism when the ground-engaging implement is raised is equal to the amount of change in the working depth detected by the working depth detection mechanism when the ground-engaging implement is lowered, the upward speed produced by the raising of

the ground-engaging implement on the basis of the working depth detected by the working depth detection mechanism becomes greater than the downward speed produced by the lowering of the ground-engaging implement on the basis of the working depth detected by the working depth detection mechanism. Compared with the downward case, in the upward case the inertia acts more readily on the ground-engaging implement, and movement of the ground-engaging implement is more likely to speed up.
Accordingly, the ground-engaging implement is raised rapidly after the working depth increases, and the drive load and travel of an automotive vehicle, which increase with the working depth, are more likely to decrease rapidly. The ground-engaging implement is lowered slowly after the working depth decreases, and rapid change in the drive load and travel of an automotive vehicle as the result of the lowering of the ground-engaging implement is less likely to occur. As a result, a drop in engine speed caused by controlling the elevation of the ground-engaging implement, and other problems are less likely to occur. Therefore, it is possible to work efficiently and comfortably.
In this aspect, a coordination mechanism is linked between the detection mechanism and the actuator provided to the drive mechanism, and the drive mechanism is operated by transmitting a displacement of the detection mechanism via the actuator.
In this aspect,
the actuator preferably has'
an actuator body switchable between a drive state for driving the
drive mechanism and a neutral state for stopping the operation of the
drive mechanism;
a drive operating element for switching the actuator body to the
drive state; and
a neutral operating element for switching the actuator body to
the neutral state; and
the link mechanism preferably has:
a drive interlock mechanism for operatively connecting the
working depth detection mechanism with the drive operating element; a neutral interlock mechanism for operatively connecting the
drive mechanism with the neutral operating element; and
an operating element interlock mechanism for operatively

connecting the drive operating element and the neutral operating
element so as interlock the neutral interlock mechanism with the
neutral operating element and to operate the drive operating element
when the ground-engaging implement is raised.
According to such an aspect, when the depth of working of the ground-engaging implement increases or decreases beyond the set working depth, the drive interlock mechanism switches the actuator body to the drive state on the basis of the working depth detected by the working depth detection mechanism. As the ground-engaging implement ascends or descends, the neutral interlock mechanism thereby returns the actuator body to the neutral state on the basis of the actuation of the drive mechanism, and the ground-engaging implement reaches the coupling height at which the working depth is at the set working depth. The ground-engaging implement is thereby made more likely to rise rapidly.
That is, when, as the ground-engaging implement is raised, the neutral interlock mechanism operates the neutral operating element and returns the actuator body to the neutral state, the neutral interlock mechanism is caused to interlock with the neutral operating element, the operating element interlock mechanism is operated, and the operating element interlock mechanism operates the drive operating element. Then, when the neutral interlock mechanism attempts to return the actuator body to the neutral state while the ground-engaging implement is raised, the drive operating element can be operated upward by using the operating element interlock mechanism. The upward speed at which the ground-engaging implement is raised by changing the unit change amount to a greater working depth detected by the working depth detection mechanism can thereby be made higher than the downward speed at which the ground-engaging implement is lowered by changing the unit change amount to a lesser working depth detected by the working depth detection mechanism, and the drive mechanism can be operated.
In this aspect, the operating element interlock mechanism preferably has a link having a slot and a catch that is operatively connected with the neutral operating element and engages the slot; and the operating element interlock mechanism is preferably configured so that the driving force from the drive mechanism is transmitted to the drive operating element via the operating element interlock mechanism by bringing the catch into contact

with one end of the slot when the ground-engaging implement is raised.
In this aspect, the operating element interlock mechanism is configured such that transmission of the driving force from the drive mechanism to the drive operating element via the operating element interlock mechanism is canceled by releasing the contact between the catch and one end of the slot when the ground-engaging implement is lowered.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of the rear of a work vehicle;
FIG. 2 is a side view of a link mechanism;
FIG. 3 is a top view of the link mechanism;
FIG. 4 is a rear view of an actuator;
FIG. 5 is a hydraulic circuit diagram of a hydraulic cylinder;
FIG. 6 is a view showing the state of operation of the actuator and the action status of the link mechanism in a state in which the depth of tilling by a tiller is the set tilhng depth;
FIG. 7 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is changed to a level less than the set tilling depth;
FIG. 8 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is returned to the set tilling depth by lowering the tiller;
FIG. 9 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is changed to a level greater than the set tilling depth; and
FIG. 10 is a view showing the state of operation of the actuator and the action status of the link mechanism after the depth of tilling by the tiller is returned to the set tilling depth by raising the tiller.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a side view of the rear of a work vehicle of an embodiment of the present invention. The work vehicle according to the embodiment of the present invention comprises a vehicle having a left-and-right pair of front wheels (not shown), a left-and-right pair of drivable rear wheels 1, 1, and a

steering unit equipped with a driver seat 2 provided at the rear of the vehicle body. The vehicle is also provided with a link mechanism 10 disposed at the rear of a vehicle body frame 3 of the vehicle. In the work vehicle according to the embodiment of the present invention, a rotary tiller 20 (below abbreviated as "tiller 20") is coupled via the link mechanism 10 to the rear of the vehicle body, thereby forming a riding-type tiller.
Specifically, as shown in FIG. 1, the link mechanism 10 comprises a left-and-right pair of lift arms 11, 11 provided so as to swing vertically at the upper portion of a transmission case 4 that forms the rear of the vehicle body frame 3; a left-and-right pair of lower links 12, 12 that extend so as to swing vertically toward the rear of the vehicle body from the lower portion of the transmission case 4; a top link 14 that extends so as to swing vertically toward the rear of the vehicle body from a top link bracket 13 provided at the rear of the transmission case 4; and a lift rod 15 that couples the lift arm 11 and the lower link 12 on the left and right sides of the link mechanism 10.
The extending ends of the left-and-right pair of lower links 12, 12 and the top Link 14 are coupled to a coupling frame 21 provided to the tiller 20. The left-and-right pair of lift arms 11, 11 are interlocked with a hydraulic cylinder 5 (see FIGS, 4 and 5) located within the transmission case 4, via a rotary pivot 16 that couples the left-and-right pair of lift arms 11, 11 to the transmission case 4.
That is, the left-and-right pair of lift arms 11, 11 are swung vertically by the rotary operation of the pivot 16 actuated by the hydraulic cylinder 5, whereby the link mechanism 10 is swung vertically related to the vehicle body frame 3 and whereby the tiller 20 is operated vertically between a lowered state in which a tilling rotor 22 of the tiller contacts the ground, and in a raised state in which the tilling rotor 22 is raised from the soil surface; and the tiller 20 in the lowered state is operated vertically relative to the vehicle body frame 3. The hydraulic cylinder 5 can thereby vertically adjust the tiller 20 relative to the work vehicle, vary the depth of tilling (referred to hereinbelow as "tilling depth") by the tilling rotor 22 of the tiller 20, and maintain constant the depth of tilling by the tiller 20 regardless of the longitudinal inclination and elevation of the work vehicle relative to the soil surface travelled.
The work vehicle is equipped with a motive power take-off shaft 6 rotatably provided to the rear of the transmission case 4, and the driving force

output by the engine (not shown) provided to the front portion of the vehicle body is transmitted from the motive power take-off shaft 6 to the tiller 20 via a rotary transmission shaft 7 that is coupled with the motive power take-off shaft 6.
As shown in FIG. 4, the work vehicle is equipped with an operating portion 30 provided to the transmission case 4 in order to operate the hydraulic cylinder 5. As shown in FIGS. 1, 2, and 6, the work vehicle is equipped with a tilling depth setting lever 8 located beside the driver seat 2, and a link mechanism S whereby a drive operating element 31 and a neutral operating element 32 (see FIG. 4) of the operating portion 30 are linked to a tilling depth detection mechanism 50 provided to the tiller 20.
The elevation of the tiller 20 in the work vehicle is thereby controlled so that the tilling depth of the tiller 20 reaches the tilhng depth set by the tilling depth setting lever 8 or a tilling depth close thereto even in the event that the vehicle body longitudinally inchnes or rises and falls relative to the travel soil surface after a front wheel (not shown) or a rear wheel 1 enters a depressed portion of the travelled soil surface or drives over an elevated portion of the travelled soil surface.
FIG. 4 is a rear view of the operating portion 30. FIG. 5 is a hydraulic circuit diagram for operating the hydraulic cylinder 5. As shown in the drawings, the operating portion 30 is configured with a drive operating element 31 and a neutral operating element 32, as well as an actuator body 33 that is provided within the transmission case 4, and a balance link 35 that links a spool operation shaft 34 of the actuator body 33 to the drive operating element 31 and the neutral operating element 32.
As shown in FIGS. 4 and 5, the actuator body 33 is equipped with a valve case 36 that is connected to the transmission case 4, as well as a main spool 37, a lowering valve 38, a relief valve 39, and an unload valve 40, which are disposed in the valve case 36. The main spool 37 is coupled with the spool operation shaft 34. An operation shaft 38a of the lowering valve 38 engages a tie rod 41 connected to the spool operation shaft 34.
The central portion of the balance link 35 is rotatably coupled with an operation arm portion 34a of the spool operation shaft 34. The drive operating element 31 is configured with a rotary support shaft portion 31a and a swing arm portion 31b supported so as to rotate integrally with the rotary support shaft portion 31a; and is rotatably supported by the rotary support

shaft portion 31a in a side wall portion 4a of the transmission case 4. A swing arm portion 31b engages one side of the balance link 35. The neutral operating element 32 is configured with a rotary support shaft portion 32a and a swing arm portion 32b that is supported so as to be able to integrally rotate with the rotary support shaft portion 32a; and is rotatably supported by the rotary support shaft portion 32a in the side wall portion 4a. The swing arm portion 32b engages the other end of the balance link 35.
FIG. 5 shows a state in which a coupling pin 42 that couples the balance link 35 and the arm portion 34a is in the neutral position. When the coupling pin 42 is in the neutral position, the main spool 37 discharges the pilot hydraulic pressure from the unload valve 40, and a tie rod 41 brings the lowering valve 38 into a closed state. The unload valve 40 then returns to the tank the hydraulic pressure from a hydraulic pump 43, and the lowering valve 38 stops the discharge of the hydraulic cylinder 5. That is, the actuator body 33 transitions to the neutral state so as to stop the hydraulic cylinder 5.
When the drive operating element 31 swings upward (U) around the axial center of the rotary support shaft portion 31a while the actuator body 33 is in the neutral state, the swing arm portion 31b of the drive operating element 31 swings about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32. Then the coupling pin 42 moves from the neutral position to the valve case 36 side, and the spool operation shaft 34 is slid upward (U) against the resistance of the downward-urging spring 44, and switches the main spool 37. The tie rod 41 then moves relative to the operation shaft 38a of the lowering valve 38 and maintains the lowering valve 38 in the closed state. The main spool 37 then supplies the pressurized oil from the hydraulic pump 43 to the hydraulic cylinder 5. The actuator body 33 transitions to the upward drive state so as to drive the hydraulic cylinder 5 to the side on which the lift arm 11 rises.
When the neutral operating element 32 then swings in rotational direction (A) around the axial center of the rotary support shaft portion 32a, the swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing arm portion 31a of the drive operating element 31, and moves to the side on which the coupling pin 42 of the balance link 35 is separated from the valve case 36. The appropriate amount of operation of the neutral operating element 32 causes the coupling pin 42 to return to the neutral position, and causes the

actuator body 33 to return to the neutral state.
When the drive operating element 31 is swung downward (D) around the axial center of the rotary support shaft portion 31a from the state in which the actuator body 33 is in the neutral state, the swing arm portion 31b of the drive operating element 31 is swung about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32. The coupling pin 42 of the balance link 35 then moves from the neutral position to the side opposite the valve case 36. The spool operation shaft 34 is slid downward (D) by a downward-urging spring 44, and the main spool 37 is switched. At the above time, the tie rod 41 pulls the operation shaft 38a of the lowering valve 38, and the lowering valve 38 transitions to the open state. The unload valve 40 then returns to the tank the hydraulic pressure from the hydraulic pump 43, and the lowering valve 38 discharges the pressurized oil of the hydraulic cylinder 5. That is, the actuator body 33 transitions to the lowering-side drive state so as to drive the hydraulic cylinder 5 to the side on which the lift arm 11 moves down. The downward-urging spring 44 is switches/urges the actuator body 33 to the lowering-side drive state.
At this time, when the neutral operating element 32 swings in rotational direction (B) around the axial center of the rotary support shaft portion 32a, the swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing arm portion 31b of the drive operating element 31, and the coupling pin 42 of the balance link 35 moves toward the valve case 36. When the amount of operation of the neutral operating element 32 is appropriate, the coupling pin 42 of the balance link 35 returns to the neutral position, and the actuator body 33 returns to the neutral state.
As shown in FIG. 1, the tilling depth detection mechanism 50 has a rotor rear cover.
That is, as shown in FIGS. 1 and 6, the rotor rear cover 50 is supported at a rotor top cover 51 by a coupling pin 52 in a configuration in which the rear of the tilling rotor 22 is covered. The rotor top cover 51 is fastened to a frame 23 of the tiller 20. The coupling pin 52 rotatably couples the upper portion of the rotor rear cover 50 to the rear end portion of the rotor top cover 51. The upper end of a spring support rod 53, whose lower end is coupled to the free end of the rotor rear cover 50, is supported to as to be able to slide vertically at a bracket 54 of a support arm 24 that extends from the frame 23.

A cover-lowering spring 55 mounted on the spring support rod 53 downwardly urges the spring support rod 53, with the bracket 54 as the reaction force member.
That is, the rotor rear cover 50 is supported so as to swing upward and downward relative to the frame 23 of the tiller 20 and around an axial center P of the coupling pin 52, which is transverse to the vehicle, and is downwardly urged by the cover-lowering spring 55 so as to contact the surface of the soil tilled by the tilling rotor 22.
A change in the tilling depth of the tiller 20 thereby causes the rotor rear cover 50 to swing up and down relative to the rotor top cover 51 and around the axial center P, and the swing angle of the rotor rear cover 50 to change relative to the rotor top cover 51. That is, the rotor rear cover 50 detects the swing angle relative to the rotor top cover 51 as the tilling depth.
FIG. 2 is a side view of the link mechanism S, and FIG. 3 is a top view of the link mechanism S. As shown in the drawings, the link mechanisms S is configured with a drive interlock mechanism 60 having a drive operation arm 61 provided so as to be able to rotate integrally with the rotary support shaft portion 31a of the drive operating element 31, a neutral interlock mechanism 70 having a neutral operation arm 71 provided so as to be able to rotate integrally with the rotary support shaft portion 32a of the neutral operating element 32, and a operating element interlock mechanism 80 having an output link 81 provided so as to be able to rotate integrally with the rotary support shaft portion 32a of the neutral operating element 32.
As shown in FIGS. 2 and 3, the drive interlock mechanism 60 is configured so as to have, in addition to a drive operation arm 61, a valve-side link 62 whose one end is coupled to the drive operation arm 61 via a coupling pin 61a; a sensor-side link 63 that is interlocked to the other end of the valve-side link 62 via an interlock pin 63a; a tie rod 64 that couples the front-side end of the vehicle body to one end of the sensor-side link 63 via a coupling pin 63b; a rod-side relay link 65 that is coupled to the end at the rear of the vehicle body of the tie rod 64 via a coupling 65a; a cable-side relay link 66 provided so as to be able to rotate integrally with the rotary pivot 65b of the rod-side relay link 65; and a sensor coupling cable 67 that couples the work vehicle-side end of an inner cable 67a to the cable-side relay link 66.
As shown in FIG. 6, the tiller-side end of the inner cable 67a of the sensor coupling cable 67 is coupled to a cable-side arm 68a of a relay 68

provided with the rotor top cover 51. The relay 68 can swing around the axial center of a coupling pin 69a on a bracket 69 provided to the rotor top cover 51. The above relay 68 is equipped with, in addition to the cable-side arm 68a, a sensor-side arm 68b that is coupled so as to be able to swing integrally with the cable-side arm 68a, and a tie rod 68c for operatively connecting the sensor-side arm 68b to the rotor rear cover 50, In the above manner, the sensor coupling cable 67 is interlocked with the rotor rear cover 50 so that the swing of the rotor rear cover 50 is transmitted as detection information to the cable-side relay link 66.
The rotary pivot 65b of the rod-side relay link 65 is rotatably supported by the top link bracket 13, The rod-side relay link 65 and the cable-side relay link 66 are swingably urged by a return spring RB supported on the rotary pivot 65b. The link is urged in the direction that pulls the sensor coupling cable 67 and pushes the tie rod 64.
As shown in FIGS. 2 and 3, the valve-side link 62 has a slot 62a provided to the side that is interlocked with the sensor-side link 63. The interlock pin 63a for operatively connecting the valve-side link 62 and the sensor-side link 63 is supported on the sensor-side link 63 so as to be slidably and rotatably inserted into the slot 62a. The end located on the side opposite from the side where the interlock pin 63a of the sensor-side link 63 is located is coupled to a support link 82 by a coupling pin 82a.
As shown in FIGS. 2 and 3, a cylindrical-shaft-shaped rotary pivot 82b of the support link 82 is rotatably supported by the tilling depth setting lever 8 via a pivot 8a; and the sensor-side link 63 is supported by the tilling depth setting lever 8 via the support link 82 and the pivot 8a.
As shown in FIGS. 2 and 3, the neutral interlock mechanism 70 is configured so as to have, in addition to the neutral operation arm 71, a tie rod 72 that rotatably couples the end of the front side of the vehicle body to the neutral operation arm 71, and a rod support rod 74 that uses a pair of positioning screws 73, 73 to couple the end portion of the tie rod 72 to the rear side of the vehicle body.
The base of the rod support rod 74 is supported at a location biased in relation to the swing axial center of the lift arm 11 at the base of the lift arm 11. As a result, the rod support rod 74 interlocks the tie rod 72 to the hydraulic cylinder 5 via the lift arm 11.
As shown in FIGS. 2 and 3, the operating element interlock mechanism

80 is configured with the output link 81, as well as a tie rod 83 one end of which is rotatably coupled to the output link 81, a relay link 84 to which the other end of the tie rod 83 is rotatably coupled, the support link 82, the sensor-side link 63, the valve-side link 62, and the drive operation arm 61.
As shown in FIG, 4, the output link 81 is coupled so as to be able to rotate integrally with the cylindrical-shaft-shaped rotary pivot 71a of the neutral operation arm 71, and is thereby coupled so as to be able to rotate integrally with the rotary support shaft portion 32a of the neutral operating element 32. As shown in FIG. 3, the relay link 84 is coupled so as to be able to rotate integrally with the pivot portion 82b of the support link 82, The relay link 84 is thereby supported by the tilling depth setting lever 8 via the rotary pivot 82b and the pivot 8a, and swings integrally with the support link 82.
That is, the drive interlock mechanism 60 interlocks the rotor rear cover 50 and the drive operating element 31 so that, as the depth of tilling detected by the rotor rear cover 50 becomes greater or less than the tilling depth set by using the tilling depth setting lever 8, the actuator body 33 of the operating portion 30 is switched to an upward or downward drive state that corresponds to the change in the detected tilling depth. The neutral interlock mechanism 70 interlocks the hydraulic cylinder 5 and the neutral operating element 32 so that, as the hydraulic cylinder 5 raises or lowers the tiller 20 to the coupling height at which the resulting tilling depth reaches the set tilling depth, the actuator body 33 of the operating portion 30 is returned to the neutral state. The operating element interlock mechanism 80 interlocks the drive operating element 31 and the neutral operating element 32 so that the upward displacement amount and the upward speed at which the tiller 20 is raised by a change in the unit change amount at which the tilling depth detected by the rotor rear cover 50 increases are greater than the downward displacement amount and the downward speed at which the tiller 20 is lowered by a change in the unit change amount at which the tilling depth detected by the rotor rear cover 50 decreases.
Fig. 6 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism s, which is in a state in which the depth of tilling by the tiller 20 is the set tilling depth;
As shown in the drawing, when the tiller 20 is at the set tilling depth, the swing angle between the rotor rear cover 50 and the rotor top cover 51 is

the reference swing angle that corresponds to the set tilling depth. Based on the tilling depth detected by the rotor top cover 51, the drive interlock mechanism 60 operates the drive operating element 31 of the operating portion 30 at the standard orientation that corresponds to the set tilling depth. Based on the swing state of the lift arm 11 as the state of operation of the hydraulic cylinder 5, the neutral interlock mechanism 70 operates the neutral operating element 32 of the operating portion 30 in the neutral orientation. The coupling pin 42 of the balance link 35 is then brought to the neutral position by the operation of the balance link 35 based on the drive operating element 31 and the neutral operating element 32. The actuator body 33 is thereby brought to the neutral state, and the hydraulic cylinder 5 is stopped.
FIG, 7 is an illustration of the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 was changed to a level less than the set tilling depth.
As the depth of tilling by the tiller 20 changes to a depth less than the set tilhng depth, the rotor rear cover 50 moves down relative to the rotor top cover 51. As a result, when the depth of tilling by the tiller 20 changes to a depth less than the set tilling depth, as shown in FIG. 7, the drive interlock mechanism 60 swings the sensor-side link 63 to the front side of the vehicle body and around the axial center of the coupling pin 82a by pushing the tie rod 64 based on the downward swinging the rotor rear cover 50, moves the interlock pin 63a of the sensor-side link 63 toward the vehicle body front of the slot 62a of the valve-side link 62, allows the drive operation arm 61 to be swung by the downward urging force of the operating portion 30, and moves the drive operating element 31 of the operating portion 30 downward from the standard orientation by using the downward urging force of the operating portion 30. At this time, the hydraulic cylinder 5 is still stopped, whereby the neutral operation arm 71 of the neutral interlock mechanism 70 brings the neutral operating element 32 of the operating portion 30 to the neutral orientation. The swing arm portion 31b of the drive operating element 31 swings about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32; the coupling pin 42 of the balance link 35 moves from the neutral position to the side (i.e., down side D) away from the valve case 36; and the actuator body 33 of the operating portion 30 switches to the downward-side drive state. As a result, the hydraulic

cylinder 5 is driven to the downward side, and the tiller 20 is lowered.
FIG. 8 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 is returned to the set tilling depth by lowering the tiller 20.
When the depth of tilling by the tiller 20 returns to the set tilling depth as the tiller 20 is lowered, the lift arm 11 descends more than at the start of the lowering operation. When the depth of tilhng by the tiller 20 returns to the set tilling depth, as shown in FIG. 8, the neutral interlock mechanism 70 thereby swings the neutral operation arm 71 by pushing the tie rod 72 based on the lowering force of the lift arm 11 as the hydraulic cylinder 5 actuating force, and actuating the neutral operating element 32 of the operating portion 30 from the standard orientation. The swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing arm portion 31b of the drive operating element 31; the coupling pin 42 of the balance link 35 moves toward the valve case 36 and returns to the neutral position; and the actuator body 33 of the operating portion 30 returns to the neutral state. The hydraulic cylinder 5 is thereby stopped and the tiller 20 is set to the coupling height at which the tilling depth is equal to the set tilling depth.
FIG. 9 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 was changed to a level greater than the set tilling depth.
As the depth of tilling by the tiller 20 changes to a deeper level than the set tilling depth, the rotor rear cover 50 rises relative to the rotor top cover 51. When the depth of tilling by the tiller 20 changes to a level greater than the set tilling depth, as shown in FIG. 9, the drive interlock mechanism 60 thereby swings the sensor-side link 63 toward the vehicle body rear and around the axial center of the coupling pin 82a by pulling the tie rod 64 based on the upward swing of the rotor rear cover 50; pressure is created toward the valve-side link 62 by the interlock pin 63a of the sensor-side link 63; the drive operation arm 61 is swung by the valve-side link 62; and the drive operating element 31 of the operating portion 30 is brought from the standard orientation to the upward side. At this time, the hydraulic cylinder 5 is stilled stopped, whereby the neutral operation arm 71 of the neutral interlock mechanism 70 brings the neutral operating element 32 of the operating portion 30 to the neutral orientation. The swing arm portion 31b of the drive

operating element 31 then swings about the side on which the balance link 35 is supported by the swing arm portion 32b of the neutral operating element 32; the coupling pin 42 of the balance link 35 moves from the neutral position toward the valve case 36 (i.e., the upward U); and the actuator body 33 of the operating portion 30 switches to the upward drive state. The hydraulic cylinder 5 is thereby driven upward and the tiller 20 is raised,
FIG. 10 is a view showing the state of operation of the operating portion 30 and the action status of the link mechanism S after the depth of tilling by the tiller 20 is returned to the set tilling depth by raising the tiller 20.
When the depth of tilling by the tiller 20 returns to the set tilling depth in conjunction with the raising of the tiller 20, the hft arm 11 is higher than at the start of the raising operation. When the depth of tilling by the tiller 20 returns to the set tilling depth, as shown in FIG. 10, the neutral interlock mechanism 70 thereby swings the neutral operation arm 71 by pulling the tie rod 72 based on the upward force of the lift arm 11 as the hydraulic cylinder 5 actuating force; and actuates the neutral operating element 32 of the operating portion 30 from the standard orientation. The swing arm portion 32b of the neutral operating element 32 swings about the side on which the balance link 35 is supported by the swing operation arm portion 31b of the drive operating element 31; the coupling pin 42 of the balance link 35 moves to the side away from the valve case 36 and returns to the neutral position; and the actuator body 33 of the operating portion 30 returns to the neutral state. The hydraulic cylinder 5 is thereby stopped and the tiller 20 is brought to the coupling height at which the tilling depth is equal to the set tilling depth.
As shown in FIGS. 7 and 8, when the lift arm 11 descends, the operating element interlock mechanism 80 does not operate the drive operating element 31 regardless of the actuation by the neutral interlock mechanism 70. That is, during descent of the lift arm 11, the output link 81 interlocked with the neutral operating element 32 swings to the left side in the drawing around the axial center of the rotary support shaft portion 32a, and the driving force of the output link 81 is transmitted to the support link 82 via the tie rod 83 and the relay link 84. The support link 82 then swings to the right in the drawing around the axial center of the pivot 8a; the sensor-side link 63 swings to the right in the drawing around the axial center of the coupling pin 63b; and the interlock pin 63a is operated to the side away from the left end of the slot 62a in the drawing. When the lift arm 11 is lowered,

the operating element interlock mechanism 80 thereby blocks the interlocking of the neutral operating element 32 and the drive operating element 31, and the application of the urging force to the drive operating element 31 is terminated.
When the swing angle of the rotor rear cover 50 is brought to the dead zone as the reference swing angle in conjunction with the lowering of the lift arm 11, the sensor-side link 63 is swung around the axial center of the coupling pin 82a by the tie rod 64 as a result of the rising of the rotor rear cover 50 relative to the rotor top cover 51, whereby the interlock pin 63a is positioned at the end of the slot 62a on the left side of the drawing, and the valve-side link 62 supports the drive operation arm 61, with the interlock pin 63a serving as the reaction force member. The neutral operation arm 71 of the neutral interlock mechanism 70 operates the neutral operating element 32. When the depth of tilling by the tiller 20 returns to the set tilling depth, the operation of the balance, link 35 by the drive operating element 31 and the neutral operating element 32 thereby allows the coupling pin 42 of the balance link 35 to be brought to the neutral position, the actuator body 33 of the operating portion 30 to be brought to the neutral state; and the hydraulic cylinder 5 to be stopped.
By contrast, as shown in FIGS. 9 and 10, when the lift arm 11 is raised, operation by the neutral interlock mechanism 70 causes the operating element interlock mechanism 80 to operate the drive operating element 31 in opposition to the downward swing of the rotor rear cover 50 relative to the rotor top cover 51. That is, when the lift arm 11 is raised, the output link 81 interlocked with the neutral operating element 32 swings to the lower-right side of the drawing around the axial center of the rotary support shaft portion 32a, and the driving force of the output link 81 is transmitted to the support link 82 via the tie rod 83 and the relay link 84. The support link 82 swings to the left side in the drawing around the axial center of the pivot 8a; the sensor-side link 63 swings to the left side in the drawing around the axial center of the coupling pin 63b; and the interlock pin 63a contacts the left end of the slot 62a in the drawing. When the lift arm 11 is raised, the operating element interlock mechanism 80 thereby interlocks the neutral operating element 32 and drive operating element 31, and the drive operating element 31 is operated to the upward side in opposition to the lowering of the rotor rear cover 50 relative to the rotor top cover 51.

When the swing angle of the rotor rear cover 50 is located in the dead zone as the reference swing angle during the raising of the lift arm 11, there is balance between the operation of the neutral operating element 32 by neutral interlock mechanism 70 and the operation of the drive operating element 31 by the operating element interlock mechanism 80. Therefore, the coupling pin 42 of the balance link 35 returns to the neutral position, the actuator body 33 of the operating portion 30 transitions to the neutral state, and the hydraulic cylinder 5 stops.
That is, when the neutral interlock mechanism 70 operates the neutral operating element 32 and returns the actuator body 33 to the neutral state in conjunction with the lowering of the lift arm 11, the neutral interlock mechanism 70 operates the output link 81 of the operating element interlock mechanism 80 by interlocking with the neutral operating element 32. At this time, the valve-side link 62 is not pushed by the interlock pin 63a due to the swing direction of the output link 81, and an operating element interlock mechanism 80 does not operate the drive operating element 32 toward the downward side. By contrast, when the neutral interlock mechanism 70 operates the neutral operating element 32 and returns the actuator body 33 to the neutral state in conjunction with the raising of the lift arm 11, the neutral interlock mechanism 70 operates the output link 81 of the operating element interlock mechanism 80 by interlocking with the neutral operating element 32. At this time, the valve-side link 62 is pressed by the interlock pin 63a due to the swing direction of the output link 81, and the operating element interlock mechanism 80 brings the drive operating element 31 to the upward side.
A comparison can thereby made between the upward displacement amount and the upward speed at which the tiller 20 is raised by a change in the unit change amount to a greater tilling depth detected by the rotor rear cover 50, and the downward displacement amount and the downward speed at which the tiller 20 are lowered by a change in the unit change amount to a lesser tilling depth detected by the rotor rear cover 50. When the comparison is made, the link mechanism S operates the hydraulic cylinder 5 in a state in which the upward displacement amount and the upward speed exceed the downward displacement amount and the downward speed, and which is brought about by the action of the operating element interlock mechanism 80; and controls the ascent and descent of the tiller 20 so that the tiller 20 is

moved more rapidly by inertial during ascent than during descent.
As shown in FIGS. 2 and 3, the base of the tilling depth setting lever 8 is rotatably coupled with the transmission case 4 via the coupling shaft 4b, and the tilling depth setting lever 8 is supported so as to swing longitudinally relative to the vehicle body around the axial center of the coupling shaft 4b. When the tilling depth setting lever 8 is swung in the above manner, the support link 82 swings the sensor-side link 63 around the axial center of the coupling pin 63a, The interlock pin 63b is then brought to the left end of the slot 62a in the drawing and is caused to press on the valve-side link 62; and either the drive operating element 31 is operated by swinging the drive operation arm 61 via the valve-side link 62, or the interlock pin 63b moves to the right of the slot 62a in the drawing and allows the drive operation arm 61 to be swung by the urging force of the spring 44 of the actuator body 33, and the drive operating element 31 is swung by the urging force of the spring 44 of the actuator body 33. The movement of the neutral position of the coupling pin 42 of the balance link 35 is then adjusted, and a positioning mechanism (not shown) for creating fuctional resistance that acts on the base of the tilling depth setting lever 8 maintains the tilling depth setting lever 8 in the operating position and maintains the neutral position of the coupling pin 42 of the balance link 35 at the movement-adjustment position.
The tilling depth setting lever 8 thereby varies and sets a shallower or deeper level for the tilling depth maintained by controlling the raising and lowering of the tiller 20 with the aid of the link mechanism S.
[Other Embodiments]
The object of the present invention can be achieved when various implements (e.g., a plow) are coupled in place of the tiller 20. The object of the present invention also is achievable by adopting a configuration in which the tiller 20 is operated upward and downward by using a motor in place of the hydraulic cylinder 5. The object of the present invention also is achievable by adopting a configuration in which the tilling depth is detected by a detection mechanism dedicated to detecting the tilling depth, in place of the rotor rear cover 50.
Accordingly, the tiller 20 and the hke are collectively referred to as the ground-engaging implement 20, the hydraulic cylinder 5 and the like are referred to as the drive mechanism 5, and the rotor rear cover 50 and the like are collectively referred to as the tilling depth detection mechanism 50.

I/We claim
1. A work vehicle, comprising:
a vehicle body supported by a plurality of wheels:
a drive mechanism for vertically moving a ground-engaging implement coupled with the vehicle body;
a working depth detection mechanism provided to the ground-engaging implement to detect a working depth of the ground-engaging implement; and
a link mechanism for coupling the detection mechanism and the drive mechanism, and operating the drive mechanism so that the working depth detected by the working depth detection mechanism is at the set working depth;
characterized in that
the link mechanism operates the drive mechanism such that an upward speed at which the ground-engaging implement is raised in response to a predetermined amount of increase in the working depth, from a set working depth, detected by the working depth detection mechanism is greater than a lowering speed at which the ground-engaging implement is lowered in response to a predetermined amount of decrease in the working depth, from a set working depth, detected by the working depth detection mechanism.
2. The work vehicle of Claim 1, wherein
the link mechanism is linked between the detection mechanism and an operating portion provided to the drive mechanism; and
the drive mechanism is operated by transmitting a displacement of the detection mechanism via the operating portion.
3. The work vehicle of Claim 2,
the operating portion having:
an operating portion body switchable between a drive state for driving the drive mechanism and a neutral state for stopping the operation of the drive mechanism;
a drive operating element for switching the actuator body to the drive state; and
a neutral operating element for switching the actuator body to the neutral state; and the link mechanism having:
a drive interlock mechanism for operatively connecting the working depth detection mechanism with the drive operating element;

a neutral interlock mechanism for operatively connecting the drive mechanism with the neutral operating element; and
an operating element interlock mechanism for operatively connecting the drive operating element and the neutral operating element so as to operatively connect the neutral interlock mechanism with the neutral operating element and to operate the drive operating element when the ground-engaging implement is raised.
4. The work vehicle of Claim 3, wherein
the operating element interlock mechanism has a link having a slot and a catch that is operatively connected with the neutral operating element and engages the slot; and the operating element interlock mechanism is configured such that the driving force from the drive mechanism is transmitted to the drive operating element via the operating element interlock mechanism by bringing the catch into contact with one end of the slot when the ground-engaging implement is raised.
5. The work vehicle of Claim 4, wherein
the operating element interlock mechanism is configured such that transmission of the driving force from the drive mechanism to the drive operating element via the operating element interlock mechanism is canceled by releasing the contact between the catch and one end of the slot when the ground-engaging implement is lowered.

Documents:

703-CHE-2008 CORRESPONDENCE OTHERS 02-02-2012.pdf

703-CHE-2008 CORRESPONDENCE OTHERS 21-06-2012.pdf

703-CHE-2008 ENGLISH TRANSLATION 02-02-2012.pdf

703-CHE-2008 EXAMINATION REPORT REPLY RECEIVED 25-09-2012.pdf

703-CHE-2008 AMENDED CLAIMS 27-06-2012.pdf

703-CHE-2008 EXAMINATION REPORT REPLY RECEIVED 27-06-2012.pdf

703-CHE-2008 FORM-3 27-06-2012.pdf

703-CHE-2008 OTHER PATENT DOCUMENT 27-06-2012.pdf

703-che-2008-abstract.pdf

703-che-2008-claims.pdf

703-che-2008-correspondnece-others.pdf

703-che-2008-description(complete).pdf

703-che-2008-drawings.pdf

703-che-2008-form 1.pdf

703-che-2008-form 18.pdf

703-che-2008-form 26.pdf

703-che-2008-form 3.pdf

703-che-2008-form 5.pdf

« Previous Patent

Next Patent »

Patent Number

253686

Indian Patent Application Number

703/CHE/2008

PG Journal Number

33/2012

Publication Date

17-Aug-2012

Grant Date

13-Aug-2012

Date of Filing

20-Mar-2008

Name of Patentee

KUBOTA CORPORATION

Applicant Address

2-47, SHIKITSUHIGASHI 1-CHOME NANIWA-KU, OSAKA-SHI OSAKA 556-8601

Inventors:

#	Inventor's Name	Inventor's Address
1	NAKAMURA, TADASHI	C/O KUBOTA CORPORATION SAKAI SEIZOSHO, 64,ISHIZUKITAMACHI SAKAI-KU, SAKAI-SHI OSAKA 590-0823
2	IWATA, NORIHIDE	C/O KUBOTA CORPORATION SAKAI SEIZOSHO, 64,ISHIZUKITAMACHI SAKAI-KU, SAKAI-SHI OSAKA 590-0823

PCT International Classification Number

F16H61/42

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2007-129483	2007-05-15	Japan