JP5087953B2 - Tractor - Google Patents

Description

  The present invention relates to a tractor that is an agricultural machine. In particular, the vehicle is provided with vehicle speed control means using a hydraulic continuously variable transmission.

In Patent Document 1, an engine speed detector that detects an engine load is provided, and when the engine speed decreases due to a work load by a rotary work machine, a hydraulic continuously variable transmission that controls traveling speed is decelerated and controlled. There is disclosed a tilling speed control means for increasing the speed of the hydraulic continuously variable transmission when the rotation speed is increased and working at a predetermined tilling speed.
JP 2003-129879 A

  In conventional engine load control, when a load is applied to the rotary working machine during tillage work, the engine rotation is reduced. The change in the engine speed is read to control the tilling speed of the rotary work machine. In this case, the reaction speed is slow because the tilling speed is reduced after the engine speed is down, and the work efficiency is reduced. Of course, there was a problem that caused engine stalls.

  The object of the present invention is to constantly sense the movement of the rotary rear cover, and when the rear cover exceeds a set value, the trunnion shaft of the hydraulic continuously variable transmission that controls the vehicle speed is operated in the deceleration direction. By returning the vehicle speed to the original position, the vehicle speed is controlled to return to the original value, thereby speeding up the control reaction without reducing the engine speed, thereby eliminating the above problem.

In order to solve the above problems, the present invention has taken the following technical means.
That is, the invention according to claim 1 is provided with a rotary work machine (R) that can be raised and lowered at the rear part of the vehicle body, and the vertical rotation angle of the rear cover (18) attached to the rotary work machine (R). A hydraulic continuously variable transmission (22) for controlling the vehicle speed based on the detection result of the rear cover sensor (22) when a rear cover sensor (22) for detection is provided and the rotation angle of the rear cover (18) exceeds a predetermined range or more. 34) When the trunnion shaft (92) is controlled in the deceleration direction and the rear cover (18) whose rotation angle exceeds a certain range returns to the predetermined tilling depth control range, the trunnion shaft (92) is brought into the predetermined speed range. The tractor is characterized by performing return control .

During tillage work, if the rotation angle of the rear cover (18) exceeds a certain range , the trunnion shaft (92) of the hydraulic continuously variable transmission (34) is decelerated based on the detection result of the rear cover sensor (22). To reduce the vehicle speed to a predetermined speed. When the rear cover (18) returns to the original position, the vehicle speed also returns to the original speed, and the tilling work can be performed efficiently while maintaining a predetermined tilling speed.

According to the first aspect of the present invention, when the rotation angle of the rear cover exceeds a certain range, the trunnion shaft is controlled to decelerate. Therefore, the vehicle speed is decelerated after the load is actually applied to the engine and the engine speed starts to decrease. Compared to what is controlled, the vehicle speed can be controlled more responsively. And, the rotation of the engine can be efficiently performed while maintaining an appropriate tillage speed without causing the engine rotation to drop.

An embodiment of the invention will be described with reference to the drawings.
In the present specification, the left and right directions in the forward direction of the work vehicle are referred to as left and right, respectively, the forward direction is referred to as front, and the reverse direction is referred to as rear.

1 is an overall side view of the tractor, FIG. 2 is a plan view of the tractor of FIG. 1, FIG. 3 is a power transmission path diagram of the transmission of the tractor of FIG. 1, and FIG. 4 is a control block diagram of the transmission.
The tractor shown in FIGS. 1 to 3 includes left and right front wheels 2 and 2 and left and right rear wheels 3 and 3 at the front and rear portions of the fuselage, and the rotational power of the engine E mounted on the front portion of the fuselage is changed within the transmission case 4. It is configured so as to be appropriately decelerated by the device and transmitted to the left and right front wheels 2, 2 and the left and right rear wheels 3, 3. A hydraulic cylinder case 5 is mounted on the rear upper part of the mission case 4, and lift arms 12, 12 constituting a part of the hydraulic lifting mechanism are pivotally supported on both left and right sides of the cylinder case 5. Has been. When hydraulic oil is supplied to the lift cylinder 8 accommodated in the cylinder case 5, the lift arm 12 rotates upward, and when it is discharged, the lift arm 12 descends.

  A steering handle 7 is supported on the handle post 6 in the center of the aircraft, and a seat 9 is provided behind the steering handle 7. A forward / reverse lever 10 is provided below the steering handle 7 to switch the advancing direction of the airframe to the front / rear direction. When the forward / reverse lever 10 is moved forward, the aircraft moves forward, and when it is moved backward, it moves backward. Further, an accelerator lever 11 is provided on the opposite side of the forward / reverse lever 10 with the handle post 6 interposed therebetween, and an accelerator pedal 15 and left and right brake pedals 16 and 17 are disposed at the right corner portion of the step floor 13. A clutch pedal 19 is disposed at the left corner of the step floor 13.

  A main transmission lever (HST lever) 20 capable of selecting a gear position from 1st to 8th is located in the left front portion of the cockpit 9 and can be selected at any of low speed, medium speed, high speed and neutral positions. The speed change lever 21 is located behind it, and a PTO speed change lever 23 capable of selecting the 1st to 3rd speeds and the neutral position is provided behind the speed change lever 21. Further, on the right side of the cockpit 9, a position lever 24 for setting the height of the rotary working machine R, an automatic tilling lever 25 for automatically setting the tilling depth of the field, and a rotary work behind these levers 24, 25. A right-up switch 27 and a right-down switch 28 of the machine R are arranged, and further behind it is a horizontal switch 29 (on the absolute horizontal position of the tractor with respect to the horizontal plane of the earth, And a backup switch 30 (when the forward / reverse lever 10 is in the reverse position, the work machine raising link 31 raises the work machine) and a rotary work machine is located behind the machine body. The link 31 is provided to connect R. The pivot side base portion of the lift arm 12 has a lift arm as a means for detecting the lift position of the rotary work machine R. The lift arm sensor 14 detects the rotation angle of the lift arm 12, and the controller 90 calculates the elevation height of the rotary work machine R. The rotary work machine R A rear cover 18 is attached to the rear end of the main cover so as to be rotatable up and down, and within a certain range, the rotation angle of the rear cover 18 is detected by the rear cover sensor 22, and the controller 90 determines the working depth of the rotary work machine R. It is configured to calculate.

  Then, when the rotation angle of the rear cover 18 exceeds a certain range or more (when the tillage work load becomes large), trunnion deceleration control means (A ) Is provided in the controller 90 in the form of a control program. That is, when the rear cover sensor 22 detects a tilling load exceeding a certain level, a control signal is output from the controller 90 to the trunnion hydraulic cylinder 93 that operates the trunnion shaft 92 in the deceleration direction. When the rear cover returns to within a predetermined tilling depth control range, the trunnion shaft also returns to within the predetermined speed range, so that tilling control can be performed while maintaining a predetermined tilling speed.

  FIG. 3 is a route diagram showing a traveling transmission system of a tractor having the hydrostatic continuously variable transmission (HST) 34 of the present embodiment. The rotational power of the engine E is transmitted to the main clutch 32 that is operated by depressing the pedal-operated clutch pedal 19 and then transmitted from the HST input shaft 33 to the HST 34. The HST 34 includes a hydraulic closed circuit 34c including a variable displacement hydraulic pump 34a and a constant displacement hydraulic motor 34b. The hydraulic pump 34a is operated by power introduced from the HST input shaft 33, and the hydraulic pump 34a is operated. The hydraulic oil 34b is supplied to the hydraulic motor 34b from the hydraulic closed circuit 34c, and the traveling output shaft 36 is driven by the hydraulic motor 34b to supply power to the meshing transmission 38. Communicate.

  The sub-transmission clutch 39 of the meshing transmission 38 is slidable in the left and right directions in FIG. 39 is transmitted from the auxiliary transmission clutch 39 to the gear 45 of the transmission shaft 43, and the rotation of the transmission shaft 43 is driven through the differential device 46 at the traveling speed of the auxiliary transmission high speed stage.

  Further, when the auxiliary transmission clutch 39 moves to the right from the position shown in FIG. 3 and the auxiliary transmission clutch 39 is engaged with the gear 45 and the medium speed gear 47 of the transmission shaft 43, the power from the travel output shaft 36 is transmitted to the gear. 41 is transmitted from the gear 49 to the sub-transmission clutch 39 via the gear 50, the gear 51, and the gear 47 sequentially, and further transmitted from the sub-transmission clutch 39 to the gear 45 of the transmission shaft 43 to rotate the transmission shaft 43. The rear wheel 3 is driven through the differential device 46 at the traveling speed of the intermediate speed stage of the sub-shift.

  When the auxiliary transmission clutch 39 further moves to the right side and engages with the gear 45 and the low speed gear 55 of the transmission shaft 43, the power from the travel output shaft 36 is transferred from the gear 49 to the gear 56 via the gear 41, and further from the gear 56. Is transmitted to the gear 57, transmitted from the gear 55 coaxial with the gear 57 to the auxiliary transmission clutch 39, and further transmitted from the auxiliary transmission clutch 39 to the gear 45 of the transmission shaft 43, and the rotation of the transmission shaft 43 is transmitted via the differential device 46. The rear wheel 3 is driven at the traveling speed of the sub-speed stage.

  Even if the sliding position of the auxiliary transmission clutch 39 is on the left or right side, the output from the transmission shaft 43 is transmitted to the front wheel output shaft 61 via the gears 53, 59, 60, etc. in order. At this time, if the hydraulic clutch 63 is connected, the front wheel 2 is driven together with the rear wheel 3 via the differential device 65, and if the hydraulic clutch 64 is connected, the front wheel speed is increased. It becomes. The hydraulic clutch 63 and the hydraulic clutch 64 are not connected together, and if the hydraulic clutch 63 and the hydraulic clutch 64 are not connected together, two-wheel drive is performed in which only the rear wheel 3 is driven.

  On the other hand, the power input from the HST input shaft 33 to the variable displacement hydraulic pump 34a is transmitted from the pump output shaft 66 to the drive system for PTO. The PTO drive system includes a PTO forward / reverse clutch 67 and a PTO auxiliary transmission clutch 68. When the tractor travels on the road, either one or both of the clutches 67 and 68 are in an unconnected state to drive the work machine. The PTO drive system is not driven.

  When working with the work implement in the field, the HST is set because the engine speed is set to the rated speed or a constant speed from the rated speed to the maximum speed by pulling the accelerator lever 11 toward the operator (front side). The input shaft 33 and the pump output shaft 66 rotate at a constant speed. The state shown in FIG. 3 is a neutral state, and the PTO shaft 69 directly connected to the pump output shaft 66 rotates together. When the PTO forward / reverse clutch 67 is slid in the left direction in the figure, the PTO forward / reverse clutch 67 is engaged with the gear 70 and the gear 71 of the PTO shaft 69, so that the power of the PTO shaft 69 is the gear 70, the PTO forward / reverse clutch 67, and the gear 71. , 71a, 72, 74, 78, β, 76, the PTO transmission shaft 75 is driven (PTO reverse rotation). When the PTO forward / reverse clutch 67 is slid to the right, the power of the PTO shaft 69 drives the PTO transmission shaft 75 via the gear 70, the PTO forward / reverse clutch 67, and the gears α, β, 76 (PTO forward rotation). To do.

  The power from the gear 78 interlocking with the driving of the gear 74 integral with the gear 72 is also transmitted to the PTO transmission shaft 75, and the gear 79 and the gear 80 are located when the PTO auxiliary transmission clutch 68 is moved to the left from the illustrated position. The gear dock 81 is engaged with a gear dock 83 provided in the PTO auxiliary transmission clutch 68 via the PTO, and the PTO first speed is obtained by the PTO drive shaft 84. When the PTO auxiliary transmission clutch 68 moves left or right from the illustrated position, power is transmitted to the PTO auxiliary transmission low speed gear 85 or the PTO auxiliary transmission high speed gear 86 that meshes in each case, and the PTO auxiliary transmission low speed gear 86 is engaged. The gear 85 → the gear 68a → the PTO drive shaft 84 obtains the PTO second speed, and the PTO auxiliary speed change high speed gear 86 → the gear 68b → the PTO drive shaft 84 obtains the PTO third speed.

  The tractor having the above-described configuration depresses the clutch pedal 19 when traveling on the road, and sets the auxiliary transmission lever 21 to a position suitable for traveling on the road (basically, the high-speed position may be set to the medium-speed position or the low-speed position). Next, the HST lever 20 is moved to an arbitrary position. The HST lever 20 can be selected from a minimum speed of 1st speed to a maximum speed of 8th speed, but the basic speed when traveling on the road is 8th speed.

  Next, the forward / reverse lever 10 is moved forward or backward, and the engine pedal is increased by stepping on the accelerator pedal 15 while slowly releasing the clutch pedal 19 (with the main clutch 32 connected). At this time, even if the accelerator pedal 15 is fully depressed, the maximum speed is restricted to the position of the maximum speed stage (8th speed) of the HST lever 20.

  Further, when working in the field, after depressing the clutch pedal 19, the sub-shift lever 21 is set to an appropriate position (basic is a low speed or medium speed position). Next, the HST lever 20 is moved to an arbitrary position (selectable from the first speed to the eighth speed according to the type of work), and the forward / reverse lever 10 is moved to the forward position. The accelerator lever 11 is moved to the pilot side (front side), and the engine speed is set to a rated speed or a maximum speed greater than the rated speed. Next, the clutch pedal 19 is moved forward (with the main clutch 32 connected). At this time, the engine speed is set between the rated speed and the maximum speed equal to or higher than the rated speed, but the working speed is regulated by the position of the HST lever 20.

  FIG. 5 shows a left side view of only the handle post 6, the airframe near the cockpit, and the HST lever 20. The HST lever 20 can change the gear position from 1st to 8th speed, and a position sensor 22a capable of detecting a position position corresponding to each speed stage is provided at the base of the lever 20. The detection value of the position sensor 20a is output to the controller 90 (FIG. 4).

  6 shows a plan view of the transmission case 91 (FIG. 6A) and a plan view of the HST 34 housed in the transmission case 91 (FIG. 6B). 7 shows a side view of the transmission case 91 as viewed from the direction of arrow A in FIG.

  As shown in FIGS. 5 to 7, a link mechanism 95 that connects the hydraulic cylinder 93 that rotates the trunnion shaft 92 of the HST 34 and the trunnion shaft 92 that protrudes outside the transmission case 91 is connected to the outer wall portion of the transmission case 91. It is attached to. The other end of the arm 95a having one end rotatably connected to the tip of the piston rod 93a of the cylinder 93 is rotatably supported on the outer wall of the transmission case 91, and the other end of the arm 95a is supported on the other end. One end of a rod 95b provided in a direction orthogonal to the arm 95a is rotatably provided, and the other end of the rod 95b is extended in a direction substantially parallel to the arm 95a through a rotatable arm 95c. The end of the adjustable rod 95d is rotatably connected.

  The other end of the rod 95d whose length can be adjusted is rotatably connected to one end of a short arm 95e, and a boss 95f is fixed to the other end of the short arm 95e. The boss 95f is fixed to the shaft q with a bolt p. The shaft q is rotatably supported with respect to the transmission case 91. A plate 95g is fixed to the axis q. The other end of the plate 95g is connected to the end of a trunnion arm 95j integral with the trunnion shaft 92 by a pin r so as to be rotatable. The end of the link arm 95h opposite to the connecting portion of the plate 95g is connected to the end of the trunnion arm 95j integrated with the trunnion shaft 92. The connecting pin r between the plate 95g and the link arm 95h is slidable in the arc-shaped elongated hole 95k1 of the fan-shaped member 95k fixed to the transmission case 91 with the axis q as a pivot. Since r is slidable only within the long hole 95k1, the rotation range of the trunnion arm 95j is also regulated within a range interlocked with the sliding of the pin r.

  By the link mechanism 95, the operation of the hydraulic cylinder 93 is interlocked with the arm 95a, the rod 95d and the like so that the trunnion arm 95j rotates together with the trunnion shaft 92. Further, the trunnion arm 95j is rotated by the cylinder 93 while the side surface of the trunnion arm 95j contacts the side surface of the roller 95m supported by the transmission case 91.

  6 shows a state in which the trunnion shaft 92 faces the swash plate 34d of the hydraulic pump 34a of the HST 34 toward the vehicle forward side, and is a plan view (FIG. 8 (a)) of the transmission case 91 of FIG. A state showing a plan view of the HST 34 housed in the transmission case 91 (FIG. 8B) shows a state where the swash plate 34d of the hydraulic pump 34a of the HST 34 is in a neutral position, and the trunnion arm 95j The neutral position of the trunnion shaft 92 is the position where the roller 95m (the roller 95m is springed in the x direction) with respect to the cam recess 95n. The roller 95m is attached to a slide pin 95q that is slidable with respect to the bracket 94, and is pressed and biased toward the cam recess side of the trunnion arm 95m (x direction) by a biasing spring 95s (see FIG. 9).

  10 is a plan view of the transmission case 91 (FIG. 10A) and a plan view of the HST 34 housed in the transmission case 91 (FIG. 10B). The state which turned the swash plate 34d of the pump 34a to the reverse side is shown.

  FIG. 11 is a diagram showing the arrangement of shift switches 10a and 10b provided at the base of the forward / reverse lever 10 and the operation mode thereof. 11 (a) and 11 (c) are layout diagrams in which the forward shift switch 10a and the reverse shift switch 10b provided at the base of the forward / reverse lever 10 operate when the forward / reverse lever 10 is in the forward position and the reverse position. FIG. 11B shows a layout when the forward / reverse lever 10 is in the neutral position and does not come into contact with either the forward shift switch 10a or the reverse shift switch 10b.

  When the HST lever 11 is tilted from the neutral position to the forward side so that the forward shift switch 10a of the forward / reverse lever 10 is operated, it is ready to move in the forward direction, and the backward shift switch 10b of the forward / backward lever 10 is operated. When the lever 11 is tilted backward from the neutral position, it is ready to move in the reverse direction.

  FIG. 12 shows a conventional example of the reverse lever reverser cam 100. When the clutch pedal is depressed, the lock pin 101 rises and locks the lock plate of the forward / reverse lever. In the conventional reverser cam, Since it is composed of one piece, it takes time to adjust the lock pin, and in particular, independent adjustment on the reverse side is difficult. In this example, as shown in FIG. 13, the reversal cam 100 is divided into three parts, 100F, 100N, and 100R, to restrict the movement of the cam. Each of the regulating cams 100F, 100N, and 100R can be easily adjusted in angle with the bolt 102, and the position of the pin can be fixed, so the number of parts can be reduced, and the cam can be fixed at all forward, neutral and reverse positions.

  The HST deceleration control means can also be applied to turning control. For example, the trunnion shaft 92 of the HST 34 is controlled to shift by an actuator (for example, a trunnion hydraulic cylinder 93) via the controller 90, and when the mode change switch is in the tilling mode, the shifting position (for example, 8th speed, When the vehicle enters a turn at the 7th speed and the 6th speed, the vehicle speed is automatically reduced to the first stage (for example, if the 6th speed is before the turn, the speed is reduced to the 5th speed).

  According to this, since the airframe does not drop the engine rotation at the time of turning, it is safe to turn with a margin. After the decelerating turn, the work implement is lowered to a predetermined tillage work position and then accelerated to the original shift position (for example, the fifth speed is increased by one step and returned to the sixth speed). In addition, when the mode change switch tries to move backward in the tillage mode (when the operating lever is operated to the reverse position), when the work implement is in the lowered state, the work implement is not moved backward, Control to start reverse after confirming the rise of. According to this, it is possible to prevent the working machine from being damaged.

  As shown in FIG. 14, (1) a trunnion arm angle sensor 92a for detecting the HST trunnion arm angle, a main shift lever position detection sensor 20a for detecting the main shift lever 20 position, a clutch pedal 19 switch, a linear lever A position lever (control lever) 24 is provided in a tractor provided with sensors 10a and 10b for detecting at least forward or reverse movement of the (forward / reverse lever) 10 and the trunnion arm angle can be adjusted by the main transmission lever 20, the linear lever 10 or the like. When raising the work lever such as raising, finger lever 26, backup, autolift, etc., the gear shift point (target value for trunnion adjustment) corresponding to the main gear shift lever is corrected to one step lower side, position lever lowered, finger gap When operating the lever, etc. Is returned to the transmission point corresponding to the over, structure to which outputs their shift points corresponding trunnion arm angle adjustment and so as to (see flow chart in FIG. 15).

  Further, in the tractor having the configuration (1), when the work implement is raised and adjusted by the depth control during the tilling control by the depth sensor 97, the shift point (the trunnion adjustment target value) corresponding to the main shift lever is further increased. When the work implement is lowered and adjusted to a predetermined value by depth control, the shift points corresponding to the main shift lever are returned and output is performed so that the trunnion arm angle adjustment corresponding to those shift points is performed. It can also be configured (see the flowchart of FIG. 16).

  Conventionally, since the HST, the main transmission lever, and the linear lever are connected in a mechanical link configuration, the HST neutral region is excessively increased in order to ensure safety. In the above-described example, it is possible to ensure safety as a previous stage when starting the engine by avoiding the connection by the mechanical link and electrically operating the connection. Raising the work equipment reduces the load and increases the vehicle speed. For this reason, decelerating saves energy. When the work implement is lowered, the load returns and the vehicle speed also returns.

Further, in the tractor having the above configuration (1), when the speed increase or deceleration adjustment is large in the case of speed change control, a correction adjustment output is performed to raise the work machine by a certain amount (for example, lift arm −10 pits). (Refer to the flowchart of FIG. 17), and after the adjustment on the raising side, the work implement is returned in stages for a certain period of time or at a predetermined speed at that time. When the shift becomes larger and the load increases, the load decreases with a slight increase in the work implement.In a tractor equipped with an output device that lowers or restores the vehicle speed by a certain amount, at least turning Sometimes when lowering the vehicle speed by a certain amount when raising the control lever, raising the finger lever, backing up, autolift, etc. The adjustment output that returns the vehicle speed after a certain period of time (for example, 0.3 seconds) (or below the Decera point) during the operation of lowering the work machine such as lowering the control lever, finger lever, etc. By performing (see the flowchart of FIG. 18), it can be configured so as not to roughen the turning site. That is, when the work implement is raised, the load is reduced and the vehicle speed is increased. At this time, when turning a full turn, because the vehicle speed is fast, the turning radius becomes narrow, and there is a problem that the ruins of the turning become rough.However, in this example, the problem caused by reducing the vehicle speed when turning as described above. Can be resolved.

  The embodiment shown in FIG. 19 to FIG. 21 relates to a traveling crawler 105 that travels while rotating an endless track band 105a between a driving wheel 105b, a driven wheel 105c, and a wheel 105d. By adopting a configuration in which the support frame 106 that supports the driving wheel 105c, the bearing member 107 that holds the wheel 105d and the like are accommodated within the crawler width L, interference with crops and straws is prevented.

  The traveling crawler 105 can freely swing about ± 5 degrees around the axis of the drive wheel 105b. However, the traveling crawler 105 may cause problems because it is free to swing, such as when pushing on soil or when used in a field. . Therefore, as shown in FIG. 20, it was possible to solve the problem by providing stoppers 108 and 108 for fixing the swing of the traveling crawler. The stopper 108 is configured to restrict the swing angle of the traveling crawler by inserting a plate 110 between the stopper rubber 109 and the base 111. Further, as shown in FIG. 21, it is preferable that the stopper rubber 109 can be taken in and out by an adjusting bolt 112 so that the swing amount of the traveling crawler can be freely changed and adjusted.

Side view of tractor Top view of tractor Traveling system power transmission path diagram Control block diagram of transmission Left side view of the main part of the tractor (A) Plan view of transmission case, (b) Plan view of HST Side view of the transmission case as seen from the direction of arrow A in FIG. (A) Plan view of transmission case, (b) Plan view of HST Side sectional view of the main part of FIG. (A) Plan view of transmission case, (b) Plan view of HST Side view showing the operating state of the forward / reverse lever "forward", "neutral" and "reverse" A perspective view of a conventional reverser cam Perspective view of the reverser cam of this example Control block circuit diagram flowchart flowchart flowchart flowchart Cutting front view of traveling crawler Side view of traveling crawler Part cut side view

18 Rear cover 22 Rear cover sensor 34 Hydraulic continuously variable transmission (HST)
90 controller 92 trunnion shaft 93 trunnion hydraulic cylinder 95j trunnion arm 95m roller 95n cam recess 95p slide pin 95s urging spring R rotary working machine A trunnion deceleration control means 90 controller 92 trunnion shaft 93 trunnion hydraulic cylinder

Claims (1)

A rotary work machine (R) that can be moved up and down is attached to the rear part of the vehicle body, and a rear cover sensor (22) that detects a vertical rotation angle of a rear cover (18) attached to the rotary work machine (R) is provided. When the rotation angle of the rear cover (18) exceeds a predetermined range , the trunnion shaft (92) of the hydraulic continuously variable transmission (34) for controlling the vehicle speed is decelerated based on the detection result of the rear cover sensor (22). Control in direction ,
A tractor characterized by performing control to return the trunnion shaft (92) to a predetermined speed range when the rear cover (18) whose rotation angle exceeds a predetermined range returns to a predetermined tilling depth control range .

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