JP2009058060A - Working vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a working vehicle with a transmission device capable of surely holding a trunnion shaft at a neutral position when a hydraulic cylinder is actuated by an operation of a back and forth lever to drive the trunnion shaft of a hydrostatic continuously variable transmission device. <P>SOLUTION: In this working vehicle, when a neutral position set by a back and forth lever 10 is a target neutral position of a trunnion shaft 92, a sensor value of a trunnion shaft position sensor 92a at the target neutral position is a reference neutral value, and the working vehicle reciprocates between a vehicle forward side and a vehicle backward side in a range near the reference neutral value plural times. Thereafter, actuation of the hydraulic cylinder 93 is controlled by a controller 90 so that the reference neutral value by the sensor value becomes a central value of the reciprocating action of the hydraulic cylinder 93, so that the target neutral position set by the back and forth lever 10 can be matched with the central value of the reciprocating action of the hydraulic cylinder 93. This can prevent the trunnion shaft 92 from being displaced from the neutral position, and can surely bring the trunnion shaft 92 to the neutral position, so as to secure a neutral stopping property. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a traveling vehicle having a transmission composed of a hydrostatic continuously variable transmission (HST) and a meshing transmission used in work vehicles such as tractors for agriculture, construction, and transportation.

A work vehicle such as a tractor including a transmission including a hydrostatic continuously variable transmission and a meshing transmission is described in, for example, Japanese Patent Application Laid-Open No. 2002-250437.
In the transmission comprising the hydrostatic continuously variable transmission and the meshing transmission of the work vehicle, the forward / reverse lever determines the forward / reverse rotation direction of the trunnion shaft, and the trunnion shaft is rotated based on the operation amount of the shift lever. The output of the hydrostatic continuously variable transmission is performed by adjusting the operating amount of the hydraulic cylinder.
JP 2002-250437 A

In the transmission, the adjustment of the rotation angle of the trunnion shaft of the hydrostatic continuously variable transmission by the transmission lever is performed by operating the trunnion shaft by the hydraulic cylinder according to the detection value of the detection sensor that detects the rotation angle of the transmission lever. This is done by adjusting the inclination (rotation) angle of the movable swash plate of the trunnion shaft. That is, the hydraulic cylinder is controlled by a controller to switch the valve to expand and contract to rotate the trunnion shaft connected to the hydraulic cylinder by a link mechanism, and the movable swash plate provided on the trunnion shaft is tilted. Is detected by a sensor and fed back to the controller.
The neutral position set by the forward / reverse switching lever may not coincide with the neutral position of the trunnion shaft, the amount of operation of which is determined by the hydraulic cylinder and the link mechanism.

  The reason for this is that, as shown in FIG. 23, as a characteristic of the hydrostatic continuously variable transmission, the trunnion shaft rotates along the solid line from the neutral position (zero point) of the trunnion shaft when the piston of the cylinder extends. When the piston of the hydraulic cylinder contracts, it operates like a dotted line, and the neutral return position of the trunnion shaft may be shifted from the zero point. Moreover, it may shift | deviate also by the play of a link.

  Therefore, since the neutral position is not corrected in the configuration described in Patent Document 1, there is a disadvantage that the neutral position is deviated. Even if the neutral position of the forward / reverse switching lever is maintained, the trunnion shaft actually moves the forward / reverse switching lever. The holding control is not always performed at the neutral position set in (1).

  An object of the present invention is to provide a transmission that can securely hold a trunnion shaft in a neutral position when a hydraulic cylinder is operated by operating a forward / reverse switching lever to drive a trunnion shaft of a hydrostatic continuously variable transmission. It is to provide a work vehicle.

The above-mentioned problem of the present invention is solved by the following means.
According to the first aspect of the present invention, in a work vehicle provided with a hydrostatic continuously variable transmission (34) for adjusting the rotation angle of the trunnion shaft (92) and outputting the power of the engine (5), the hydrostatic type A trunnion shaft rotating hydraulic cylinder (93) for determining the rotation angle of the trunnion shaft (92) of the continuously variable transmission (34), and provided between the trunnion shaft (92) and the hydraulic cylinder (93), A trunnion shaft position sensor (92a) for detecting the rotational angle position of the trunnion shaft (92) by the operation of the cylinder (93), a forward / reverse lever (10) for switching the traveling direction of the vehicle to the front / rear direction, 10) When the neutral position set in 10) is set as the neutral target position of the trunnion shaft (92), the sensor value of the neutral target position by the trunnion shaft position sensor (92a) is neutral. As a quasi-value, a hydraulic cylinder (so that the neutral reference value based on the sensor value becomes the center value of the reciprocating operation of the hydraulic cylinder (93) after the range near the neutral reference value is reciprocated a plurality of times toward the vehicle forward side and the vehicle reverse side. 93) and a controller (90) for performing operation control.

  According to a second aspect of the present invention, a control output for operating the hydraulic cylinder (93) of the controller (90) is a pulse output composed of an on time and an off time, and the controller (90) is a trunnion shaft position sensor. The sensor value of (92a) is controlled so as to have a shorter on-time after reaching the neutral reference value vicinity range than before reaching the neutral reference value vicinity range, and further reaches the neutral reference value vicinity range. 2. The work vehicle according to claim 1, wherein a correction is made to gradually increase the short on-time from the vehicle forward side to the vehicle reverse side or from the vehicle reverse side to the vehicle forward side.

  For example, the control output of the controller (90) is set as a pulse output, and after the trunnion shaft (92) reaches the neutral reference value vicinity range, the hydraulic cylinder (93) operates reliably (on the neutral reference value vicinity range). Width from the neutral reference value of the detected value of the trunnion axis position sensor (92a) on the vehicle forward side and the detected value of the trunnion axis position sensor (92a) on the reverse side of the vehicle (Difference) increases, and it may take time until the detection value of the trunnion shaft position sensor (92a) reaches the neutral reference value. On the other hand, even if the on-time is short, the operation of the hydraulic cylinder (93) is delayed, and it takes time to reach the neutral reference value. In addition, if the vehicle moves beyond the neutral dead band, the vehicle body starts to move at a very low speed.

  However, according to the present invention, the neutral position set by the forward / reverse lever (10) is set as the neutral target position of the trunnion shaft (92), and the trunnion shaft position sensor (92a) corresponding to the neutral target position is used. Neutral control is performed to operate the hydraulic cylinder (93) with the sensor value of the neutral value as a neutral reference value. The sensor value of the trunnion shaft position sensor (92a) is within the vicinity of the neutral reference value a plurality of times on the vehicle forward side and the vehicle reverse side. The controller (90) controls the operation amount of expansion and contraction of the hydraulic cylinder (93) so that the neutral reference value is obtained after the reciprocation.

  According to the second aspect of the invention, the on-time after reaching the neutral target position vicinity range is made shorter than that before reaching the neutral target position vicinity range, and further, the short on-time is corrected to be gradually increased. Thus, the change in the value of the trunnion shaft position sensor (92a) in the vicinity of the neutral target position can be reduced. Then, by performing the on-time increase correction, the operation of the hydraulic cylinder (93) is accelerated and can be quickly set to the neutral reference value. However, if the operation of the hydraulic cylinder (93) is too fast, as described above, the neutral reference value is obtained. In order to ensure the neutral reference value, it is slow as a short on-time as a whole. However, if the on-time increase is corrected little by little and the operation of the hydraulic cylinder (93) is slightly accelerated, good.

  According to the first aspect of the present invention, the sensor value by the trunnion shaft position sensor (92a) at the neutral target position set by the forward / reverse lever (10) is set as the neutral reference value, and the neutral reference value by the sensor value is determined by the hydraulic cylinder ( 93), the controller (90) controls the operation of the hydraulic cylinder (93) so as to be the center value of the reciprocating motion of 93), so that the neutral target position set by the forward / reverse lever (10) and the hydraulic cylinder (93) The center value of the reciprocating motion can be matched, and the trunnion shaft (92) can be prevented from shifting from the neutral position, so that the trunnion shaft (92) can be surely brought to the neutral position, and neutral stopping performance can be achieved. Secured.

  According to the invention described in claim 2, in addition to the effect described in claim 1, a change in the value of the trunnion shaft position sensor (92a) in the vicinity of the neutral reference position is reduced, and the trunnion shaft can be accurately and quickly completed. (92) can be set to the neutral position, and the neutral stop performance is improved as compared with the conventional case.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In this 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.
Hereinafter, a tractor will be described as an example of a work vehicle. 1 is an overall side view, FIG. 2 is a plan view of the tractor of FIG. 1, FIG. 3 is a power 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 front wheels 2 and 2 and rear wheels 3 and 3 in the front and rear portions of the airframe, and appropriately reduces the rotational power of the engine 5 mounted on the front portion of the airframe by a transmission in the transmission case. Thus, the front wheels 2 and 2 and the rear wheels 3 and 3 are communicated.

  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. Below the steering handle 7 is provided a forward / reverse lever 10 for switching 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. 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 of the step floor 13 to provide a step floor. A clutch pedal 19 is disposed at the left corner portion of 13.

A shift lever 20 capable of selecting a gear position from 1st speed to 8th speed is located in the left front portion of the cockpit 9. A sub shift lever 21 capable of selecting any one of a low speed position, a medium speed position, a high speed position, and a neutral position is provided thereafter. Further, a PTO speed change lever 23 capable of selecting the 1st to 3rd speeds and the neutral position is provided on the rear side. Further, on the right side of the cockpit 9, a position lever 24 for setting the height of a working machine (not shown), an automatic tilling depth lever 25 for automatically setting the tilling depth of the field, and behind these levers 24, 25. Is provided with a right-up switch (horizontal manual switch extension) 27 and a right-down switch (horizontal manual switch contraction) 28 of the work implement, and an automatic horizontal switch (horizontal sensitivity switch) 29 (horizontal with respect to the horizontal surface of the earth). And a back-up switch 30 (when the forward / reverse lever 10 is in the reverse position, the lifting hydraulic cylinder works and the work implement raising link 31 raises the work implement). Further, the link 31 for connecting a work machine (not shown) is provided behind the machine body.
Further, a horizontal changeover switch 105 (FIG. 14) for switching in order of automatic horizontal (the same function as the automatic horizontal switch 29), manual, parallel control, and tilt is also provided at an appropriate position.

  FIG. 3 is a diagram showing a traveling transmission system of a tractor having the hydrostatic continuously variable transmission 34 of the present embodiment. The rotational power of the engine 5 is transmitted to the main clutch 32 that is operated by depressing the pedal-operated clutch pedal 19 and then transmitted from the hydrostatic continuously variable transmission input shaft 33 to the hydrostatic continuously variable transmission 34. . The hydrostatic continuously variable transmission 34 includes a hydraulic closed circuit 34c having a variable displacement hydraulic pump 34a and a constant displacement hydraulic motor 34b, and is introduced from an input shaft 33 of the hydrostatic continuously variable transmission. The hydraulic pump 34a is operated by motive power, and pressure oil corresponding to the inclination angle of the swash plate 34d provided in the hydraulic pump 34a is supplied from the hydraulic closed circuit 34c to the hydraulic motor 34b, and the travel output shaft 36 is supplied by the hydraulic motor 34b. To drive the power to the meshing transmission 38.

  The sub-transmission clutch 39 of the meshing transmission 38 can slide to the left and right in FIG. 3, and when it is in the illustrated position, the power from the travel output shaft 36 is transmitted from the high-speed gear 42 to the sub-transmission clutch via the gear 41. 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 is moved 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 subtransmission clutch 39 through the gear 50, the gear 51, and the gear 47 sequentially, and further transmitted from the subtransmission clutch 39 to the gear 45 of the transmission shaft 43. The movement of the rear wheel 3 is driven at the traveling speed of the intermediate speed stage through the differential device 46.

  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 at the same time, and if the hydraulic clutch 63 and the hydraulic clutch 64 are not connected together, only the rear wheel 3 is driven.

  On the other hand, the power input from the hydrostatic continuously variable transmission input shaft 33 to the variable displacement hydraulic pump 34a is transmitted from the pump output shaft 66 to the PTO drive system. 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 accelerator lever 11 is pulled toward the operator side (front side) and the engine speed is set to the rated speed, or a constant speed from the rated speed to the maximum speed. The hydraulic continuously variable transmission input shaft 33 and the pump output shaft 66 rotate at a constant rotation 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 meshes 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. , The PTO transmission shaft 75 is driven through the gear 71a, the gear 72, the gear 74, the gear 78, the gear 77, and the gear 76 sequentially (PTO reverse rotation). When the PTO forward / reverse clutch 67 is slid in the right direction in the figure, the power of the PTO shaft 69 drives the PTO transmission shaft 75 through the gear 70, the PTO forward / reverse clutch 67, the gear 73, the gear 77, and the gear 76 sequentially. (PTO normal rotation).

  The power from the gear 78 interlocking with the driving of the gear 74 integrated with the gear 72 is also transmitted to the PTO transmission shaft 75, and when the PTO auxiliary transmission clutch 68 is in the position moved to the left most from the illustrated position, the gear 79 and the gear The gear dock 81 is engaged with the gear dock 83 provided in the PTO auxiliary transmission clutch 68 via 80, 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 gear 85, gear 68a. When the power is sequentially transmitted to the PTO drive shaft 84, the PTO second speed is obtained, and when the power is sequentially transmitted to the gear 86, the gear 68b and the PTO drive shaft 84, the PTO third speed is obtained.

  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 shift lever 20 is moved to an arbitrary position. The speed change 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 (eight speed) of the speed change 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 shift 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 transmission lever 20.

  Note that the accelerator pedal 11 is used instead of the accelerator pedal 15 when the work implement is used in the field. Further, when traveling on the road, the accelerator pedal 15 is used and the accelerator lever 11 is not used. When driving on the road, the accelerator pedal 15 can be operated in the same way as when driving a car, and the engine rotation must be kept constant when working in the field. . Therefore, the accelerator lever 11 is operated during the work, and even if the hand is released from the accelerator lever 11 during the work, it does not return to the original position. Therefore, it is possible to maintain a constant engine speed by maintaining the operated accelerator position.

  FIG. 5 shows a left side view of only the handle post 6, the airframe in the vicinity of the cockpit, and the speed change lever 20. FIG. 6 shows an enlarged view of the vicinity of the base of the speed change lever 20. The speed change lever 20 can change the speed stage 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).

  7 and 8 are plan views of the transmission case 91 (FIGS. 7A and 8A) and a plan view of the hydrostatic continuously variable transmission 34 housed in the transmission case 91. FIG. The figure (FIG.7 (b), FIG.8 (b)) is shown. FIG. 9 is a side view of the transmission case 91 as viewed from the direction of arrow A in FIG. As shown in FIGS. 5 to 9, a link mechanism 95 that connects the hydraulic cylinder 93 that rotates the trunnion shaft 92 of the hydrostatic continuously variable transmission 34 and the trunnion shaft 92 that protrudes outside the transmission case 91 is provided. It is attached to the outer wall portion of the transmission case 91.

  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 longitudinal direction of the arm 95a is rotatably provided, and the other end of the rod 95b is substantially parallel to the arm 95a via a rotatable short arm 95c. The end of the rod 95d, whose length can be adjusted in the direction, is pivotally 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 95q with a bolt 95p. The shaft 95q is rotatably supported with respect to the transmission case 91, and a plate 95g is fixed to one end of the shaft 95q. The other end of the plate 95g is rotatably connected to a link arm 95h via a pin 95r, and the link arm 95h is rotatably connected to a cam 95j integrated with the trunnion shaft 92. Here, the cam 95j is fixed to the boss 95s, and the boss 95s is fixed to the trunnion shaft 92 by a bolt 95t.

  The plate 95g and the link arm 95h are connected by a pin 95r, and the connecting portion by the pin 95r has an arc-shaped elongated hole 95k1 of a fan-like member 95k fixed to the transmission case 91 with a shaft 95q as a pivot. Since the pin 95r is slidable only in the long hole 95k1, the rotation range of the cam 95j is also restricted within the range interlocked with the sliding of the pin 95r.

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

  The state shown in FIG. 7 shows a state in which the trunnion shaft 92 faces the swash plate 34d of the hydraulic pump 34a of the hydrostatic continuously variable transmission 34 toward the vehicle forward side, and is a plan view of the transmission case 91 of FIG. FIG. 8A) and a plan view of the hydrostatic continuously variable transmission 34 housed in the transmission case 91 (FIG. 8B) show the hydraulic pressure of the hydrostatic continuously variable transmission 34. The state where the swash plate 34d of the pump 34a is directed to the neutral position is shown, and the position where the roller 95m fits into the recess 95j1 of the cam 95j is the neutral position of the trunnion shaft 92. The roller 95m is pressed by a spring from the x direction in FIG. 10 shows a plan view of the transmission case 91 (FIG. 10A) and a plan view of the hydrostatic continuously variable transmission 34 housed in the transmission case 91 (FIG. 10B). The state shows a state in which the swash plate 34d of the hydraulic pump 34a of the hydrostatic continuously variable transmission 34 is disposed facing backward.

  FIG. 11 is a view showing the arrangement and operating modes of the forward shift switch 10a and the reverse shift switch 10b provided at the base of the forward / reverse lever 10. As shown in FIG. 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.

  The operating position of the forward / reverse lever 10 can be detected by the forward shift switch 10a and the reverse shift switch 10b. As shown in FIG. 11, when the forward / reverse lever 10 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. When the forward / reverse lever 10 is tilted from the neutral position to the reverse side so that the switch 10b is operated, it is ready to move in the reverse direction. It should be noted that acceleration in the forward and backward directions of the vehicle is only performed by the shift lever 20.

FIG. 12 shows a control example for controlling the trunnion shaft 92 to the neutral target position, and FIG. 13 shows a detailed view of the operation between (a) and (b) of FIG.
According to the present embodiment, when the neutral position set by the forward / reverse lever 10 is the neutral target position of the trunnion shaft 92, the sensor value of the trunnion shaft position sensor 92a corresponding to the neutral target position is used as the neutral reference value. Neutral control for operating the hydraulic cylinder 93 is performed.

  Then, the extension (forward side) solenoid 130 of the hydraulic cylinder 93 is set such that the sensor value of the trunnion shaft position sensor 92a reciprocates a plurality of times in the vicinity of the neutral reference value toward the vehicle forward side and the vehicle reverse side a plurality of times. The controller 90 controls the operation of the retracting (reverse drive side) solenoid 131 (FIG. 14).

  FIG. 12 shows that the neutral reference value of the trunnion axis position sensor 92a is 512 (bits), the range near the neutral reference value is ± C (bits) and ± D (bits) from the neutral reference value, and pulse output data C (bits) And pulse output data D (bits) (C> 0, D> 0, D <C). Note that the neutral reference value of the trunnion shaft position sensor 92a is not limited to this value.

When the target of the hydraulic cylinder 93 that operates the trunnion shaft 92 is a neutral reference value, a reciprocating operation is performed a specified number of times in the vicinity of the neutral reference value from the neutral reference value to the forward side and the reverse side. In addition, in FIG. 12, the example which implemented the reciprocating operation 5 times is shown (Y part of FIG. 12).
Then, after performing the specified number of reciprocating operations, the dead zone of the pulse output is set to almost 0 (± 0) for a while (for example, about 10 seconds) (indicated by Z in FIG. 12). Further, when the value of the trunnion axis position sensor 92a is near neutral (512 ± C bits) during near-neutral control, the pulse output data C is changed to pulse output data D (D <C).

  This operation is performed in order to bring the trunnion shaft 92 into the neutral position due to the characteristic of the structure of the hydrostatic continuously variable transmission 34 that the phenomenon that a deviation may occur between the operation start position and the stop position of the hydraulic cylinder described in FIG. is necessary.

  According to FIG. 12, the width from the neutral reference value by the reciprocating operation of the vehicle forward side and the vehicle reverse side is constant (± D), but the width from the neutral reference value is gradually reduced as the vehicle reciprocates. You may let them.

  Thus, the sensor value by the trunnion shaft position sensor 92a at the neutral target position set by the forward / reverse lever 10 is set as the neutral reference value, and the neutral reference value by the sensor value becomes the central value of the reciprocating operation of the hydraulic cylinder 93. 90 controls the operation of the hydraulic cylinder 93, so that the neutral target position set by the forward / reverse lever 10 and the central value of the reciprocating operation of the hydraulic cylinder 93 can be matched, and the trunnion shaft 92 is moved from the neutral position. The trunnion shaft 92 can be surely brought to the neutral position by preventing the deviation, and the neutral stopping property is ensured.

  As a condition for the above operation, the neutral position (detected by the forward / reverse lever position sensor (forward shift switch 10a, reverse shift switch 10b)) is set by the forward / reverse lever 10, and the target value by the trunnion shaft position sensor 92a is neutral. When the reference value (512 bits) is reached, or when the detection value by the trunnion axis position sensor 92a is not within the neutral dead band (512 ± 2). The dead zone is ± 2 bits in the example of FIG. 12, but is not limited to this value.

  The neutral target value is set so that the sensor value of the trunnion axis position sensor 92a reaches the neutral reference value vicinity range immediately after the start of the control output before reaching the neutral reference value vicinity range and has a shorter on-time. The pulse on time in the vicinity of the reference value is preferably set to a very short on time whether the electromagnetic valve reacts or not, and further, the short on time is corrected to be gradually increased. That is, the on-time correction is applied little by little in a short time, and the trunnion shaft turning hydraulic cylinder 93 is operated at an extremely low speed.

  When the trunnion shaft 92 is operated with an on-time in which the hydraulic cylinder 93 operates reliably even after reaching the neutral reference value vicinity range (the same long on-time as before reaching the neutral reference value vicinity), the trunnion on the vehicle forward side The width (difference) between the detected value of the shaft position sensor 92a and the detected value of the trunnion shaft position sensor 92a between the vehicle reverse side and the detected value of the trunnion shaft position sensor 92a becomes a neutral reference value. It may take time. On the other hand, even if the on-time is short, the operation of the hydraulic cylinder 93 is delayed, and it takes time to reach the neutral reference value.

  However, according to the present configuration, the trunnion axis position in the neutral reference value vicinity range is corrected by shortening the on-time after reaching the neutral reference value vicinity range and further increasing the short on-time gradually. A change in the value of the sensor 92a can be reduced. Then, by performing the on-time increase correction, the operation of the hydraulic cylinder 93 is accelerated and can be quickly set to the neutral reference value. However, if the operation of the hydraulic cylinder 93 is too fast, the neutral reference value is passed as described above. Therefore, in order to ensure the neutral reference value, it is preferable to slightly increase the on-time gradually by slightly correcting the on-time increase, but to slightly speed up the operation of the hydraulic cylinder 93.

  FIG. 13 shows an operation between (a) and (b) of FIG. 12 (the sensor value of the trunnion shaft position sensor 92a changes from the position of the stopper 93e on the vehicle forward side to the position of the stopper 93f on the vehicle backward side). It is a detailed diagram, the on time after reaching the neutral reference value vicinity range is shortened to 15 msec (on time before reaching the neutral reference value vicinity range is about 30 ms), and further, 16 msec, 17 msec, 18 msec on-time correction Is shown when 1 msec is added at a time. Note that the on-time after reaching the neutral reference value vicinity range is not limited to 15 msec, and when the on-time correction is applied little by little, the range may be 2 ms to 5 ms instead of 1 msec.

Details of the pulse output increase correction will be described.
The sensor value of the trunnion shaft position sensor 92a is between the stopper 93e provided at the maximum extension setting position on the forward side of the piston rod 93a of the hydraulic cylinder 93 for trunnion shaft rotation and the stopper 93f provided at the minimum shortening setting position on the reverse side. When the pulse output of the trunnion shaft turning hydraulic cylinder 93 continues in the same direction and in the same cycle, the on-time increase correction of the pulse output is performed.

Further, as a correction condition, the sensor value (TRn) detected from the trunnion shaft position sensor 92a is within the range of the position of the reverse-side stopper 93f ≦ TRn ≦ the position of the forward-side stopper 93e, and in the same direction with the same cycle. In this case, it is assumed that the pulse output continues for 4 mbit or more in 500 msec. The standard of 4 bits is the slowest speed at which the hydraulic cylinder 93 starts to move, and varies depending on the hydraulic capacity (output) of the hydrostatic continuously variable transmission 34 of the tractor.
The correction amount for the on-time increase correction increases the on-time by 1 msec every 500 msec. The pulse output cycle is fixed.

  The correction reset condition is when a request for output in the opposite direction occurs, that is, when the output changes from the forward side to the reverse side or from the reverse side to the forward side, and when 200 msec has passed after entering the dead zone. The accuracy is improved when the reset is executed.

  First, the initial value of the on time is set to a short on time of 15 msec. When the on-time is short, the change in the value of the trunnion axis position sensor 92a in the range near the neutral reference value can be reduced.

As shown in FIG. 13, when the sensor value of the trunnion shaft position sensor 92a changes from the vehicle forward side to the vehicle reverse side, the change amount of the sensor value is 4 bits between the first 500 msec and the third 500 msec. Therefore, the above condition of not changing in the output direction (reverse side of the vehicle) by 4 bits or more is satisfied. Therefore, the on time is further increased by 1 msec from the initial value of 15 msec to 16 msec, 17 msec and 18 msec.
In the fourth and subsequent 500 msec, the output direction (reverse side of the vehicle) changes by 4 bits or more, so the on-time increase correction is stopped and 18 msec is left.

  When the piston rod 93a of the trunnion shaft turning hydraulic cylinder 93 reaches the reverse side stopper 93f with the on time remaining at 18 msec, the correction is reset by the above correction condition, and the on time returns to the initial value 15 msec. On-time increase correction when the sensor value of the trunnion shaft position sensor 92a changes from the vehicle reverse side to the vehicle forward side based on the same conditions as when the sensor value of the trunnion shaft position sensor 92a changes from the vehicle reverse side to the vehicle reverse side. Do.

  In this way, by shortening the on-time after reaching the neutral reference value vicinity range and further increasing the on-time gradually, the change of the value of the trunnion shaft position sensor 92a in the neutral reference value vicinity range can be reduced. Can be reduced. Therefore, the trunnion shaft 92 can be brought to the neutral position with high accuracy and in a short time, and the performance of stopping more neutrally is improved.

  In the example shown in FIG. 12, the dead band of the pulse output is set to almost 0 (± 0) for a while (for example, about 10 seconds) after the reciprocating operation for the specified number of times. It is preferable to make the trunnion shaft position sensor 92a slightly vibrate in the vicinity of the neutral reference value by making it very narrow (about 0 bit) (the trunnion position sensor 92a follows as a result of the fine vibration of the hydraulic cylinder 93). .)

  If the position at which the trunnion shaft 92 finally stops when the specified number of reciprocations are finished is shifted to the vehicle forward side or the vehicle reverse side, the vehicle may start at some timing. When the on-time and off-time are repeatedly vibrated repeatedly for a short time and then stopped at the neutral target position after a certain period of time, the trunnion shaft 92 accurately stops at the neutral position. Positioning accuracy is improved and neutral stopping performance is stabilized (can be neutrally stopped with better stability).

FIG. 14 shows another example of a control block diagram of the transmission for the tractor shown in FIG.
Each switch and dial and their sensors are shown on the left side (input side) across the controller 90, and solenoids are shown on the right side (output side).

  These switches are switches that are turned on (on) when pressed and turned off (turned off) when pressed again. However, when the function of the switch is automatically turned off when the neutral reference value check mode, which will be described later, is finished, the switch is turned on when the switch is pressed, and the switch itself is pressed even if the switch is turned off again. It is a switch that does not enter the state (even if it is on during the check mode, it automatically turns off from on when the check mode ends, so it will not turn on unless you press it again next time).

  The horizontal changeover switch 105 can perform horizontal control of the work machine. The horizontal changeover switch 105 is turned on to start automatic horizontal control of the work implement, and when turned off, the automatic horizontal control of the work implement is stopped. The horizontal manual switch extension 27 and the horizontal manual switch contraction 28 are switches used when the horizontal changeover switch 105 is turned off, and are switches for manually swinging the working machine to the left and right (rolling) with respect to the machine body. is there. The work implement is tilted to the right (or left) by the horizontal manual switch extension 27, and the work implement is tilted to the left (or right) by the horizontal manual switch shrinkage 28.

  The three-point changeover switch 103 selects the three-point changeover switch 103 of the switch box by selecting the mounting hole of the work equipment lifting lift cylinder 31. Select 1 for category 1 work machines (when attaching to the front hole of the lower link), and select 2 for category 2 work machines (when attaching to the rear hole of the lower link).

  The horizontal sensitivity switch 106 is a switch for switching the operation sensitivity of the automatic horizontal control device of the work machine. When the horizontal sensitivity switch 106 is pressed, the operation sensitivity becomes dull and the movement of the automatic horizontal control becomes slow. When the horizontal sensitivity switch 106 is pressed again, the operation sensitivity is restored.

  In addition, the auto sensitivity switch 107 is a switch that is normally used for tilling depth control (lifting and lowering of the rotary), but according to the present embodiment, it is a switch that is used in a check mode to be described later. Any switch can be used in the check mode, and the auto sensitivity switch 107 is an example.

  Forward / reverse lever forward detection sensor (forward shift switch) 10a, forward / reverse lever reverse detection sensor (reverse shift switch) 10b, trunnion arm angle sensor 92a (trunnion shaft position sensor), main transmission lever position detection sensor 20a (of the transmission lever 20) The position sensor), the clutch switch 97 and the like are as described above.

  Electrical signals from these switches, dials, sensors, and the like are input to the controller (CPU) 90 via the input interfaces 122 and 123. The controller 90 is provided with an A / D converter 90d, a memory (RAM) 90b, a flash memory 90c, and a D / A converter 90e, and processes and stores input electric signals. In addition, an electric signal is transmitted from the controller 90 to the nonvolatile memory 135, and a detection value from a sensor or the like is stored, and further, an electric signal is transmitted and received between the communication devices 136.

  On the output side, an extension (advance side) solenoid 130, a contraction (reverse side) solenoid 131, a buzzer 133, and the like of the trunnion shaft turning hydraulic cylinder 93 are provided via an output interface 125.

Then, the controller 90 is based on the state of the shift lever position sensor 20a and the forward / reverse lever shift switches 10a and 10b (the forward / reverse advancement detection sensor 10a and the forward / reverse advancement detection sensor 10b) and the detection value of the trunnion shaft position sensor 92a. The expansion / contraction of the hydraulic cylinder 93 is controlled. When adjusting the trunnion shaft 92 to the reverse side, the controller 90 operates the retracting (reverse side) solenoid 131 of the trunnion shaft rotating hydraulic cylinder 93 to move the piston rod 93a of the trunnion shaft rotating hydraulic cylinder 93 to the reverse side (contracting). When the trunnion shaft 92 is adjusted to the forward side, the extension (forward side) solenoid 130 of the trunnion shaft rotating hydraulic cylinder 93 is operated to move the piston rod 93a of the trunnion shaft rotating hydraulic cylinder 93. Control to move to the forward side (extension side).
Further, a buzzer 133 (FIG. 14) is provided on the output side of the controller 90 to notify when the trunnion shaft turning hydraulic cylinder 93 is not in the neutral position.

  By the way, the conventional tractor is connected to the hydrostatic continuously variable transmission 34, the shift lever 20 and the forward / reverse lever 10 with a mechanical link mechanism. The neutral range of the step transmission 34 is excessive. Further, when the work implement is raised, the load on the engine is reduced, and the vehicle speed of the tractor is increased. Therefore, in this case, it is preferable to reduce the vehicle speed in order to save energy. On the other hand, if the work implement is lowered, the load on the entire engine will return.

  However, if the neutral range is excessive, there is a problem that fine adjustment of the trunnion shaft 92 by the shift lever 20 and the forward / reverse lever 10 cannot be performed and fine control cannot be performed. In addition, by taking the neutral range excessively, even though a signal is being output forward or backward, the time during which the vehicle does not move is prolonged, and the vehicle starts moving when the driver tries to get off the vehicle for confirmation. It is necessary to ensure safety because there is a problem with it. Furthermore, the operation of adjusting the vehicle speed as the working machine is raised or lowered is complicated and time-consuming. In addition, in the case of the mechanical link mechanism, the link mechanism will shift due to the vibration of the fuselage. In addition, there is a drawback that the link mechanism is twisted due to the vibration of the fuselage and the movement becomes slow, or the operation load of the levers 10 and 20 becomes heavy due to the influence of rust.

  Therefore, according to the present embodiment, the neutral reference value and the front and rear end reference value of the trunnion shaft 92 are avoided by avoiding the connection of the mechanical link mechanism such as the hydrostatic continuously variable transmission 34, the transmission lever 20, and the forward / reverse lever 10. By providing a check mode such as the above and electrically operating each mechanism, the movement of the lever and the position of the trunnion are accurately synchronized, and safety can be ensured as a pre-stage when the engine is started.

  15 and 16 show a flow of a control example (trunnion shaft adjustment mode) for adjusting the reference value of the position sensor 92a at the rotational position of the trunnion shaft 92 of the tractor of FIG. FIG. 15 is a flow for shifting to the trunnion axis adjustment mode (previous stage), and FIG. 16 is a flow when shifting to the trunnion axis adjustment mode.

  First, the tractor key is turned on to start the engine 5, and both the check switch 115 and the G-type determination switch 114 are turned on. The check switch 115 is a switch for shifting to the check mode, and may be a plurality of switches. The G-type determination switch 114 is a switch for determining whether or not the tractor is a hydrostatic continuously variable transmission (HST) mounted machine.

Next, the forward / reverse lever 10 is set to the neutral position, the clutch pedal 19 is depressed, the clutch switch 97 (FIG. 4) is turned on (clutch disengagement), and a predetermined switch (in accordance with the flow of FIG. The horizontal sensitivity switch 106 is turned on. Then, after 1 second, the operation shifts to a trunnion shaft adjustment mode for adjusting the reference value of the position sensor 92a at the rotational position of the trunnion shaft 92.
Note that when the check switch 115 and the G-type determination switch 114 are not both on, or when the forward / reverse lever 10 is not in the neutral position, normal control processing is performed.

  It is inadvertent that the flow (in the previous stage) for shifting to the trunnion axis adjustment mode is provided and the transition to the trunnion axis adjustment mode is made when all the conditions shown in the flow of FIG. 15 are met. This is to prevent transition to the trunnion axis adjustment mode.

  In this trunnion axis adjustment mode, the neutral reference value of the trunnion axis position sensor 92a is adjusted, the reference value on the vehicle forward side and the reference value on the vehicle reverse side are adjusted, and the adjusted reference value and The neutral reference value of the original trunnion shaft position sensor 92a before shipment from the factory, the reference value of the vehicle forward side and the design value of the reference value of the vehicle reverse side are collated, and the adjusted reference value is within the design value range ( The buzzer 133 notifies that it is normal or not) (out of range).

  As shown in FIG. 16, when the trunnion shaft adjustment mode is started, at this point, the forward / reverse lever 10 is in the neutral position, so that the controller 90 extends (forward) solenoid 130 and trunnion of the trunnion shaft rotating hydraulic cylinder 93. Since no signal is output to the contraction (reverse drive side) solenoid 131 of the shaft turning hydraulic cylinder 93, both solenoids 130 and 131 are in an OFF state.

  When both the horizontal changeover switch 105 and the horizontal sensitivity switch 106 turned on in the flow of FIG. 15 are turned off, the buzzer 133 is sounded for a predetermined time (about 5 seconds) to alert the operator. In order to reset the neutral reference value, the correction value of the neutral reference value that has been stored in the nonvolatile memory 135 is cleared once, the correction value is initialized (± 0), and written to the nonvolatile memory 135 ( Step A).

  Next, a predetermined switch (the horizontal sensitivity switch 106 and the clutch pedal 19 (the clutch switch 97 (FIG. 4) is turned on and the vehicle is ready to run) according to the flow of FIG. 16) is turned on, and after 1 second, the trunnion shaft The current detection value detected from the position sensor 92a is stored in the nonvolatile memory 135 as a neutral reference value (a position where the roller 95m is fitted in the recess 95j1 of the cam 95j in FIG. 8B) (step B). In this way, the neutral reference value is newly determined in a state where the roller 95m is fitted in the recess 95j1 of the cam 95j.

  Then, the controller 90 outputs to the extension side of the piston rod 93a of the trunnion shaft turning hydraulic cylinder 93, that is, operates the extension (advance side) solenoid 130 of the trunnion shaft turning hydraulic cylinder 93. As a result, the piston rod 93a is actuated toward the vehicle forward side and hits the stopper 93e. When the piston rod 93a hits the stopper 93e, the detected value of the trunnion shaft position sensor 92a (also referred to as a trunnion arm angle sensor) becomes a constant value on the vehicle forward side, and the sensor detected value that has stopped changing is taken as the maximum reference value on the forward side. Store in the non-volatile memory 135 (step C).

  Next, when the controller 90 outputs to the contraction side of the piston rod 93a, that is, the contraction (reverse side) solenoid 131 of the trunnion shaft rotating hydraulic cylinder 93 is operated. As a result, the piston rod 93a is moved backward in the vehicle and hits the stopper 93f. When the piston rod 93a hits the stopper 93f, the detected value of the trunnion shaft position sensor 92a becomes a constant value on the reverse side of the vehicle as well as the forward side, and the sensor detection value that does not change changes to the non-volatile memory 135 as the maximum reference value on the reverse side. (Step D).

Thus, the operating range of the piston rod 93a is determined by determining the respective maximum reference values on the vehicle forward side and the vehicle reverse side.
After step A, when the horizontal sensitivity switch 106 and the clutch switch 97 are off, the flow on the left side of FIG. In this flow, when the operator operates the horizontal manual switch extension 27 and the horizontal manual switch contraction 28, the controller 90 outputs to the extension side and the contraction side of the piston rod 93 a, and the trunnion shaft turning hydraulic cylinder 93 is extended ( This is a flow for determining the neutral reference value of the trunnion shaft rotating hydraulic cylinder 93 by operating the contraction (reverse driving side) solenoid 131 of the forward side solenoid 130 and the trunnion shaft rotating hydraulic cylinder 93 in the sense of the operator. Next, a predetermined switch (the horizontal sensitivity switch 106 and the clutch pedal 19 (the clutch switch 97 (FIG. 4) is turned on and the vehicle is ready to run) according to the flow of FIG. 16) is turned on, and after 1 second, the trunnion shaft In step B, the current detection value detected from the position sensor 92a is stored in the nonvolatile memory 135 as the neutral reference value in this case.

  Further, when the trunnion shaft 92 returns to the neutral position in step E in the flow on the right side of FIG. 16, the process proceeds to step F, and the neutral reference value of the trunnion shaft rotating hydraulic cylinder 93 and the reference values of the forward side and the reverse side ( Whether or not the reference values stored in steps B, C, and D) deviate from the original neutral reference value of the trunnion shaft rotation hydraulic cylinder before the factory shipment, and the design values of the reference values on the forward and reverse sides. Determine.

  If it does not deviate from the design value, that is, if it is within the range of the design value, the buzzer 133 informs that it is normal for a predetermined time (for example, about 1 to 2 seconds), and each reference value deviates from the design value. Then, the buzzer 133 performs continuous output and notifies that it is abnormal.

  According to the present embodiment, the notification is made by the buzzer 133, but notification means such as a lamp or a monitor display may be used. Further, a plurality of buzzers 133 may be provided for normal notification and abnormality notification, and a single buzzer 133 can be handled by changing the notification form (mode) in the case of normality and abnormality. For example, it is only necessary to change the strength (magnitude) of sound, voice, music, timbre, etc., or make continuous or intermittent sounds.

  As described above, the mechanical stoppers 93e and 93f (FIG. 9) are provided on the maximum forward side and the maximum reverse side of the shift lever 20, so that the trunnion shaft 92a is controlled in the adjustment mode when the trunnion shaft position sensor 92a is checked. The reference values on the forward and reverse sides are detected almost automatically, and the trunnion shaft 92a is controlled. When the forward and reverse reference values are within the range of the design values of the neutral, maximum forward position and maximum reverse position, it is normal, and if it deviates from the design value, it is normal. By discriminating whether or not the neutral, forward maximum position, and reverse maximum position can be adjusted, it is possible to recognize whether or not adjustment is possible by the buzzer 133. The purpose of this flow is to design the neutral position, maximum forward position, and maximum reverse position. If it deviates from the value, correction is performed, and if it does not deviate, correction is not performed.

Also, the neutral reference value of the trunnion shaft 92 can be determined by the following method.
17 and 18 show another control example for adjusting the reference value of the position sensor of the rotation position of the trunnion shaft of the tractor of FIG. 1 (a trunnion axis adjustment mode different from the examples shown in FIGS. 15 and 16). The flow of is shown. FIG. 17 is a flow for shifting to the trunnion axis adjustment mode (previous stage), and FIG. 18 is a flow when shifting to the trunnion axis adjustment mode.

First, similarly to the example shown in FIG. 15, the tractor key is turned on to start the engine 5, and both the check switch 115 and the G-type determination switch 114 are turned on.
Next, the forward / reverse lever 10 is set to the neutral position, the clutch pedal 19 is depressed, the clutch switch 97 (FIG. 4) is turned on (clutch disengagement), and a predetermined switch (in accordance with the flow of FIG. Turn on the three-point selector switch 103). Then, after 1 second, the operation shifts to a trunnion shaft adjustment mode for adjusting the reference value of the position sensor 92a at the rotational position of the trunnion shaft 92.

  As described above, in the trunnion axis adjustment mode shown in FIGS. 17 and 18 as well, as in the example shown in FIGS. 15 and 16, it is inadvertent by providing a flow (previous stage) for shifting to the trunnion axis adjustment mode. The transition to the trunnion axis adjustment mode is prevented.

  As shown in FIG. 18, when the trunnion shaft adjustment mode is started, at this point, the forward / reverse lever 10 is in the neutral position, so that the controller 90 extends (forward) solenoid 130 of the trunnion shaft rotating hydraulic cylinder 93 and Since both the solenoids 130 and 131 are not output to the contraction (reverse drive side) solenoid 131 of the trunnion shaft turning hydraulic cylinder 93, both solenoids 130 and 131 are in an OFF state.

When both the horizontal changeover switch 105 and the three-point changeover switch 103 turned on in the flow of FIG. 17 are turned off, the buzzer 133 is output for a predetermined time.
Further, in order to reset the neutral reference value, the neutral reference value correction value that has been stored so far is once cleared, the correction value is initialized (± 0), and written to the nonvolatile memory 135 (step H).

  Next, when both the horizontal changeover switch 105 and the three-point changeover switch 103 remain off and a predetermined switch, for example, the horizontal manual switch extension 27 is turned on and the horizontal manual switch contraction 28 is turned off, the controller 90 rotates the trunnion shaft. Output to the extension side of the piston rod 93a of the dynamic hydraulic cylinder 93, that is, the extension (advance side) solenoid 130 of the trunnion shaft rotating hydraulic cylinder 93 is operated.

  When both the horizontal changeover switch 105 and the three-point changeover switch 103 are turned on when the vehicle starts moving forward (reverse driving may be performed first) (when the predetermined switch is pressed, the output stops and the piston rod 93a 18, the buzzer 133 is output for a predetermined time, and the position of the forward piston rod 93a at this time is detected by the trunnion shaft position sensor 92a, and the detected value is advanced. The reference value (neutral reference value (1)) is stored in the memory (RAM) 90b (step I).

  This step I is for confirming that the trunnion shaft 92 has moved forward from the neutral reference value, that is, that the piston rod 93a of the hydraulic cylinder 93 currently being operated is forward. Since it is abnormal for the vehicle to move backward when outputting to the extension side of the piston rod 93a of the trunnion cylinder 93, it is confirmed whether the output to the piston rod 93a and the operation of the vehicle are normal.

  In addition, after step H, when both the horizontal changeover switch 105 and the three-point changeover switch 103 are off and the horizontal manual switch contraction 28 is turned on and the horizontal manual switch extension 27 is turned off, the controller 90 rotates the trunnion shaft. Output to the contraction side of the piston rod 93a of the hydraulic cylinder 93 for movement, that is, the contraction (reverse side) solenoid 131 of the trunnion shaft rotation hydraulic cylinder 93 is operated.

  When both the horizontal changeover switch 105 and the three-point changeover switch 103 are turned on when the vehicle moves backward (in this case, the vehicle moves forward when moving backward), the output stops and the piston rod 93a stops when the predetermined switch is pressed. In this case, the position of the backward piston rod 93a is detected by the trunnion shaft position sensor 92a, and the detected value is used as a reference value (neutral reference value (1)) for the reverse side (memory) (RAM) 90b. (Step I).

  This step I is for confirming that the trunnion shaft 92 has moved to the reverse side from the neutral reference value, that is, that the piston rod 93a of the hydraulic cylinder 93 currently operated is on the reverse side. Since it is abnormal for the vehicle to move forward when output to the contraction side of the piston rod 93a of the trunnion cylinder 92, it is confirmed whether the output to the piston rod 93a and the operation of the vehicle are normal.

  On the other hand, after step H, when both the horizontal changeover switch 105 and the three-point changeover switch 103 are turned on, an output for shifting to the right side of the flow of FIG. 18 and turning on the buzzer 133 for a predetermined time is performed, and the trunnion shaft position sensor 92a The detected current value to be detected is stored in the memory (RAM) 90b as a neutral reference value (1) (step I).

Next, when both the horizontal selector switch 105 and the three-point selector switch 103 are turned off, the same processing as the previous (left side) flow is performed, and the reference value on the forward side or the reverse side is set as the neutral reference value (2) in the memory (RAM ) 90b (step J).
That is, when the horizontal manual switch extension 27 is turned on in the left flow of FIG. 18, the forward reference value becomes the neutral reference value (1), and when the horizontal manual switch contraction 27 is turned on in the right flow, the reverse drive is performed. The reference value on the side becomes the neutral reference value (2).

  On the other hand, when the horizontal manual switch contraction 28 is turned on in the left flow of FIG. 18, the reverse reference value becomes the neutral reference value (1), and when the horizontal manual switch extension 27 is turned on in the right flow, the vehicle moves forward. The reference value on the side becomes the neutral reference value (2).

Although the movement of the lever 20 is electrically detected, if the backlash still occurs in the link mechanism 95, the tractor may move forward or backward regardless of the movement of the piston rod 93a on the expansion side and the contraction side. . Further, the shift position of the lever 20 and the actual speed are shifted.
However, when the horizontal manual switch extension 27 is turned on in this way, the vehicle starts to move forward, and when the horizontal manual switch contraction 28 is turned on, the vehicle starts to move backward, so that the operation of the piston rod 93a and the operation of the tractor are performed. Can be confirmed, and if there is a malfunction, it can be detected early and safety can be further enhanced.

  After step H, if both the horizontal selector switch 105 and the three-point selector switch 103 are kept on, the current detected value detected from the trunnion shaft position sensor 92a is the neutral reference value (1), the neutral reference value ( 2). The values at the time when the horizontal switch 105 and the three-point switch 103 are pressed are stored. At this time, the operator's hand is away from the switch.

  The average value of the forward reference value and the reverse reference value (the neutral reference value (1) in step I and the neutral reference value (2) in step J) detected by the trunnion shaft position sensor 92a in this way is neutral. The reference value is stored in the nonvolatile memory 135 (step K).

  If it deviates from the design value of the position sensor position of the neutral position, the maximum position on the forward side, and the maximum position on the reverse side, the buzzer 133 continuously outputs and notifies that it is abnormal. If it is within the range of the design value, the buzzer 133 notifies the normality for a predetermined time (for example, about 1 to 2 seconds).

  The mechanical link mechanism that connects the hydrostatic continuously variable transmission 34, the shift lever 20, and the forward / reverse lever 10 wears when the driving time of each mechanism becomes longer due to the use of the tractor. When the neutral range of the hydrostatic continuously variable transmission 34 changes due to wear, adjustment of the sensors (trunion shaft position sensor 92a, forward / reverse lever advance detection sensor 10a, forward / reverse lever reverse detection sensor 10b, and shift lever position sensor 20a) Is required.

  However, by adopting this configuration, even if a long period of time has elapsed due to the use of the tractor, the manipulator adjustment time is reduced by correcting the neutral reference value detected by the trunnion shaft position sensor 92a, and the trunnion shaft 92 When adjusting to the neutral position, the accuracy of the neutral adjustment can be improved. Then, by distinguishing whether the adjusted neutral reference value is within the range of the original design value according to different notification forms of normal and abnormal, the sensor input side of the mechanical link mechanism or the like (input of the controller 90) It is possible to confirm at that time whether or not the adjustment is possible.

Also, the neutral reference value of the trunnion shaft 92 can be determined by the following method.
FIG. 19 shows another control example for adjusting the reference value of the position sensor 92a of the rotational position of the trunnion shaft 92 of the tractor of FIG. 1 (a trunnion axis adjustment mode different from the examples shown in FIGS. 16 and 18). The flow of is shown. FIG. 19 is a flow in the case of shifting to the trunnion axis adjustment mode, and the flow (in the previous stage) for shifting to the trunnion axis adjustment mode is the same as that in FIG.

As shown in FIG. 19, when the trunnion axis adjustment mode is started, when the predetermined switch (both the horizontal changeover switch 105 and the three-point changeover switch 103 turned on in the flow of FIG. 17) is turned off, the buzzer 133 is turned on for a predetermined time. Output.
Then, the controller 90 reads the neutral reference correction value of the trunnion shaft 92a stored in the nonvolatile memory 135 (step M).

  Next, when the forward / reverse lever 10 is operated in the forward direction, the correction value of the neutral reference value detected from the trunnion shaft position sensor 92a is corrected by a predetermined amount (for example, +1 (bit)). When the forward / reverse lever 10 is operated to the reverse side, the correction value of the neutral reference value detected from the trunnion shaft position sensor 92a is corrected by a predetermined amount (for example, -1 (bit)).

Further, every time the forward / reverse lever 10 is tilted forward, the neutral reference value correction value is increased by a predetermined amount, and every time the forward / backward lever 10 is tilted backward, the neutral reference value correction value is decreased by a predetermined amount. Is also possible. The neutral reference value can be corrected up to the upper limit (piston rod 93a hits the stopper 93e) on the forward side and the lower limit (piston rod 93a hits the stopper 93f) on the reverse side.
When the horizontal changeover switch 105 and the three-point changeover switch 103 are pressed, the buzzer 133 is output for a predetermined time, and the neutral reference correction value is stored in the nonvolatile memory 135 (step N).

  If it does not deviate from the design value of the position sensor position of the neutral position, the maximum position on the forward side, the maximum position on the reverse side, that is, within the range of the design value, the buzzer 133 informs that it is normal for a predetermined time, If each reference value deviates from the design value, the buzzer 133 outputs continuously and notifies that it is abnormal.

  The mechanical link mechanism that connects the hydrostatic continuously variable transmission 34, the shift lever 20, and the forward / reverse lever 10 wears when the driving time of each mechanism becomes longer due to the use of the tractor. When the neutral region of the hydrostatic continuously variable transmission 34 changes due to wear, the sensors (trunion shaft position sensor 92a, forward / reverse lever advance detection sensor 10a, forward / reverse lever reverse detection sensor 10b, shift lever position sensor 20a) Adjustment is required.

  However, the adoption of this configuration eliminates the need for adjustment of sensors by automatically correcting the neutral reference value detected by the trunnion shaft position sensor 92a even when a long period of time has elapsed. It is possible to improve the accuracy of neutral adjustment when making adjustments. Then, by distinguishing whether the adjusted neutral reference value is within the range of the original design value according to different notification forms of normal and abnormal, the sensor input side of the mechanical link mechanism or the like (input of the controller 90) It is possible to confirm at that time whether or not the adjustment is possible.

20 and 21 show a flow of a control example for adjusting the reference value detected by the position sensor 20a of the transmission lever 20 of the tractor of FIG. FIG. 20 is a flow for shifting to the adjustment mode for the position sensor 20a reference value of the shift lever 20 (previous stage), and FIG. 21 is a flow for shifting to the adjustment mode for the position sensor 20a reference value of the shift lever 20 It is.
Next, a method for adjusting the reference value of the first to eighth speed position sensor 20a of the speed change lever 20 will be described. The speed change lever 20 can change from the first speed to the eighth speed, and adjusts the positions of the first speed and the eighth speed, which are the minimum speed and the maximum speed.

  First, similarly to the example shown in FIG. 15, the tractor key is turned on to start the engine 5, and both the check switch 115 and the G-type determination switch 114 are turned on.

    Next, when a predetermined switch (for example, the auto sensitivity switch 107 according to the flow of FIG. 20) is turned on for 1 second, the shift lever 20 shifts from the first speed to the eighth speed position sensor 20a reference value adjustment mode. To do.

  As described above, even in the adjustment mode of the reference value of the position sensor 20a of the shift lever, the transition to the adjustment mode is prevented by providing a (previous stage) flow for shifting to the adjustment mode. .

  As shown in FIG. 21, when the adjustment mode of the position sensor 20a reference value of the shift lever 20 is started and the position of the shift lever 20 is set to the eighth speed position, the current position is detected and stored. The current position is read a plurality of times to obtain an average value.

    When the auto sensitivity switch 107 is turned on, the buzzer 133 is output for a predetermined time, and the average value of the eighth speed position of the position sensor 20a is stored in the nonvolatile memory 135 as the reference value of the eighth speed position of the shift lever 20 ( Step Q).

  Next, when the position of the speed change lever 20 is set to the 1st speed position, the sensor value of the position sensor 20a at the current 1st speed position is read a plurality of times to obtain an average value.

    When the auto sensitivity switch 107 is turned on, the buzzer 133 is turned on for a predetermined time, and the average value of the first speed position of the position sensor 20a is stored in the nonvolatile memory 135 as the reference value of the first speed position of the shift lever 20 ( Step R).

    If the 1st speed position and the 8th speed position obtained as described above do not deviate from the design value of the position of the shift lever 20, the buzzer 133 notifies the normality for a predetermined time, and each reference value deviates from the design value. If this is the case, the buzzer 133 is continuously output to notify that it is abnormal.

  Depending on the rigidity of the rod of the speed change lever 20 and the lever guide, a bend between the speed change lever 20 and the position sensor 20a may occur, and the value detected by the position sensor 20a may deviate.

    However, as in this configuration, the values detected by the position sensor 20a at the 1st speed position and the 8th speed position of the speed change lever 20 are read a plurality of times, and the reference values for the 1st speed position and the 8th speed position are averaged by a plurality of average values. By doing so, the positions of the 1st speed position and the 8th speed position can be determined with high accuracy. When the 1st speed position and the 8th speed position are determined, the position of the speed stage between them can be determined by equally distributing.

  Thus, the performance of control of the trunnion shaft 92 can be improved by increasing the accuracy of each reference position of each speed stage between the first speed to the eighth speed of the speed change lever 20. Further, by distinguishing whether each reference position of the 1st speed position and the 8th speed position is within the range of the design value by different notification modes of normal (predetermined time output) and abnormal (continuous output), the shift lever 20 The accuracy of the operation position is improved as compared with the prior art.

FIG. 22 shows a flow of another control example of the tractor of FIG. Specifically, in order to enable travel even when the flow when the trunnion shaft 92 that is not in the neutral position is automatically returned to the neutral position when the engine 5 is started and the detection value by the trunnion shaft position sensor 92a is an abnormal value. The flow of is shown.
Further, when the engine 5 is started, even if the forward / reverse lever 10 is in the neutral position, if the trunnion shaft 92 is deviated from the neutral position, it is conceivable that the aircraft suddenly starts traveling as the engine 5 is started.

  In order to prevent this, even when the forward / reverse lever 10 is in the neutral position when the engine 5 is started, if the trunnion shaft 92 is deviated from the neutral position, the trunnion is notified by the buzzer 133 or the like. It is preferable that the shaft 92 is automatically set to the neutral position.

  For example, when the power of the tractor is turned on, when the forward / reverse lever 10 is in the neutral position, the buzzer 133 may continuously notify and the piston rod 93a of the trunnion shaft 92 may be controlled to be in the neutral position. This operation is performed before the tractor moves. This is because the tractor may move if the engine 5 is turned off and the engine is driven again in a state where the auxiliary transmission lever 21 is engaged and the forward / reverse lever 10 is engaged.

  The detected value by the trunnion axis position sensor 92a is an abnormal value (for example, when the position sensor is abnormal, only one signal of 0V or 5V is input) or a reference value (neutral reference value, forward movement). When all of the reference values such as the side reference value and the reverse side reference value) are abnormal values (ie, when they deviate from the original design values), if the forward / reverse lever 10 is operated to the forward side, the controller 90 operates for a certain period of time. (For example, about 30 minutes) Output to the forward side (the extension side of the piston rod 93a of the hydraulic cylinder 93 of the trunnion shaft 92), and the extension (forward side) solenoid 130 of the hydraulic cylinder 93 for turning the trunnion shaft is operated.

  When the forward / reverse lever 10 is operated to the reverse side, the controller 90 outputs to the reverse side (for example, the contraction side of the piston rod 93a of the hydraulic cylinder 93 of the trunnion shaft 92) for a certain time (for example, about 30 minutes). Control is performed to operate the solenoid 131 of the cylinder 93 (reverse side). This is because it is necessary to move the tractor in the case of an emergency even in such an abnormality.

  When the controller 90 determines that the detected value by the trunnion shaft position sensor 92a is normal during traveling as described above, all reference values such as reference values (neutral reference values, forward reference values, reverse reference values, etc.) are obtained. ) Is not adjusted (for example, if the wire is disconnected, the trunnion sensor value may become a normal value due to current flowing through the wire due to vibration or the like during traveling), the trunnion shaft position sensor 92a The output of the forward / reverse solenoids 130 and 131 is restricted even within a certain time (for example, about 30 minutes) depending on the detected sensor value (even if the trunnion sensor value is a normal value, it is restricted if it deviates from the design value). .).

The above configuration will be described with reference to the flowchart of FIG.
First, the tractor key is turned on to start the engine 5, and the trunnion safety mode that automatically returns the trunnion shaft 92 that is not in the neutral position to the neutral position when the engine 5 is started is set. If the safety flag is present in step T, continuous output is performed by the buzzer 133. If the forward / reverse lever 10 is in the neutral position, the trunnion shaft 92 is adjusted to the neutral position, and the trunnion safety mode is terminated.

  By the trunnion safety mode, the neutral position can be automatically set even when the trunnion shaft 92 is deviated from the neutral position. If there is no safety flag in step T, the process proceeds to step U and shifts to the right flow. In this flow, in order to enable traveling even when the detection value by the trunnion axis position sensor 92a is an abnormal value or when the reference value (neutral reference value, forward reference value, reverse reference value, etc.) is an abnormal value. This is a flow (travel mode when the trunnion sensor is abnormal).

  Even if the detected value by the trunnion axis position sensor 92a is an abnormal value or the reference value is an abnormal value, if this abnormal value is not avoided, the tractor cannot run and cannot move from the field. Can not be returned to a predetermined place (such as a garage), so that the tractor can travel for a certain period of time.

First, in step U, the detection values (neutral reference value, forward reference value, reverse reference value, etc. of any of the trunnion axis position sensor 92a (if any one of them is an abnormal value, the process proceeds to YES)). If it is a value, continuous output by the buzzer 133 is performed.
When the forward / reverse lever 10 is operated to the forward side, the controller 90 outputs to the extension side of the piston rod 93a of the trunnion shaft turning hydraulic cylinder 93 for a certain time, that is, the trunnion shaft turning hydraulic cylinder 93 is extended (forward). Side) Solenoid 130 is activated and the vehicle moves forward.

  Further, when the forward / reverse lever 10 is operated to the reverse side, the controller 90 outputs to the contraction side of the piston rod 93a of the trunnion shaft rotation hydraulic cylinder 93 for a certain time, that is, the trunnion shaft rotation hydraulic cylinder 93 is contracted (reverse side). ) The solenoid 131 is operated, and the vehicle moves backward. Then, when the count becomes zero by the timer, the running is stopped. If you want to run again, perform the above operations. In Step V, if the vehicle is moving forward or backward, the process proceeds to NO. If the vehicle is not traveling (during stop), the process proceeds to YES, and the travel mode when the trunnion sensor is abnormal is terminated.

  In step V, when the process proceeds to NO, it is determined whether or not the detected value by the trunnion shaft position sensor 92a is a normal value. And even if the trunnion shaft position sensor 92a shows a normal value during traveling, if the normal value is far from the design value, the predetermined speed is restricted. On the other hand, if the detection value of the trunnion shaft position sensor 92a is not far from the design value, the speed is not restricted.

In the conventional tractor, when the power is turned on, the forward / reverse lever 10 is in the neutral position. However, if the piston rod 93a of the trunnion shaft 92 is on the forward side or the reverse side, the tractor moves against the driver's will.
Further, even in the event of an abnormality such as when the detected value by the trunnion shaft position sensor 92a is an abnormal value, a means for moving the tractor as an emergency operation is required in an emergency.

Furthermore, when the reference values (neutral reference value, forward reference value, reverse reference value, etc.) are not adjusted by the trunnion axis position sensor 92a (for example, before adjustment at the factory or replacement of the controller 90) In case of deviation from the design value), the trunnion shaft position sensor 92a regulates the forward / reverse output to prevent deterioration and damage of the components of the mechanical stopper (93e, 93f (Fig. 9)) it can.
By adopting this configuration, it is possible to improve the safety of control of the trunnion shaft 92 and the escape function in an emergency.

  The present invention can be used as a work vehicle such as a tractor for agriculture, construction, and transportation.

It is a left view of the tractor of one Example of this invention. It is a top view of the tractor of FIG. It is a power diagram of the transmission of the tractor of FIG. It is a control block diagram of the transmission of the tractor of FIG. FIG. 2 is a left side view of only the handle post, the fuselage in the vicinity of the cockpit, and the shift lever of the tractor of FIG. FIG. 5 is an enlarged view of a base portion of the speed change lever of FIG. 4. FIG. 7 is a plan view (FIG. 7A) of the transmission case of the tractor during forward movement in FIG. 1 and a plan view of the hydrostatic continuously variable transmission housed in the transmission case (FIG. 7B). is there. FIG. 8 is a plan view of the transmission case of the tractor in the neutral state of FIG. 1 (FIG. 8A) and a plan view of the hydrostatic continuously variable transmission housed in the transmission case (FIG. 8B). is there. It is the side view of the transmission case seen from the arrow A direction of Fig.8 (a). FIG. 10 is a plan view (FIG. 10A) of the transmission case of the reverse tractor in FIG. 1 and a plan view of the hydrostatic continuously variable transmission housed in the transmission case (FIG. 10B). is there. The base of the forward / reverse lever indicates whether the forward / reverse lever of the tractor in FIG. 1 is in the forward position (FIG. 11 (a)), the neutral position (FIG. 11 (b)), or the reverse position (FIG. 11 (c)). It is a figure which shows arrangement | positioning of the shift switch provided in and its operation | movement aspect. It is the figure which showed the example of control which controls a trunnion axis | shaft to a neutral target position. It is the figure which showed the detailed figure of operation | movement between ab of FIG. It is the figure which showed the other example of the control block diagram of the transmission of the tractor of FIG. It is the flow which showed the example of control which adjusts the reference value of the position sensor of the rotation position of the trunnion axis | shaft of the tractor of FIG. It is the flow which showed the example of control which adjusts the reference value of the position sensor of the rotation position of the trunnion axis | shaft of the tractor of FIG. It is the flow which showed another control example which adjusts the reference value of the position sensor of the rotation position of the trunnion axis | shaft of the tractor of FIG. It is the flow which showed another control example which adjusts the reference value of the position sensor of the rotation position of the trunnion axis | shaft of the tractor of FIG. It is the flow which showed another control example which adjusts the reference value of the position sensor of the rotation position of the trunnion axis | shaft of the tractor of FIG. FIG. 3 is a flowchart showing a control example for adjusting a position sensor reference value of a shift lever of the tractor of FIG. 1. FIG. FIG. 3 is a flowchart showing a control example for adjusting a position sensor reference value of a shift lever of the tractor of FIG. 1. FIG. It is the flow which showed another example of control of the tractor of Drawing 1. It is a figure explaining that there exists hysteresis in the rotation angle of the trunnion shaft of the hydrostatic continuously variable transmission using the hydraulic cylinder and the link mechanism of the prior art.

Explanation of symbols

2 Front wheel 3 Rear wheel 5 Engine 6 Handle post
7 steering handle 9 seat 10 forward / reverse lever 10a forward shift switch 10b reverse shift switch 11 accelerator lever 11a throttle sensor 13 step floor 15 accelerator pedal 16, 17 brake pedal 19 clutch pedal 20 shift lever 20a position sensor 21 auxiliary shift lever 23 PTO shift Lever 24 Position lever 25 Automatic tilling lever 27 Right up switch (horizontal manual switch extended)
28 Lower right switch (horizontal manual switch retracted)
Reference Signs List 30 Backup Switch 31 Work Machine Lifting Link 32 Main Clutch 33 Hydrostatic Continuously Variable Transmission Input Shaft 34 Hydrostatic Continuously Variable Transmission 34a Hydraulic Pump 34b Hydraulic Motor 34c Hydraulic Closed Circuit 34d Swash Plate 36 Traveling Output Shaft 39 Subshift Clutch 41 Gear 42 High speed gear 43 Transmission shaft 45 Gear 46 Differential device 47 Medium speed gear 49, 50, 51, 53 Gear 55 Low speed gear 56, 57, 59, 60 Gear 61 Front wheel output shaft 63 Hydraulic clutch 64 Hydraulic clutch 65 Differential device 66 Pump output shaft 67 PTO forward / reverse clutch 68 PTO auxiliary transmission clutch 68a, 68b Gear 69 PTO shaft 70, 71, 71a, 72, 73, 74 Gear 75 PTO transmission shaft 76, 77, 78, 79, 80 Gear 81 , 83 Gear dock 84 PTO drive shaft 85 PTO auxiliary speed change Gear 86 PTO subtransmission high speed stage gear 90 controller 90a EEPROM
90b memory (RAM) 90c flash memory 90d A / D converter 90e D / A converter 91 transmission case 92 trunnion shaft 92a position sensor 93 trunnion shaft rotating hydraulic cylinder 93a piston rod 93c arm 93d rotating shaft 93e, 93f stopper 95 Link mechanism 95a, 95c Arm 95b Rod 95d Rod 95e Short arm 95f Boss 95g Plate 95h Link arm 95j Cam 95j1 Recess 95k Fan-shaped member 95k1 Long hole 95m Roller 95p Bolt 95q Shaft 95r Pin 95s Bos 95t Bolt 97 Clutch switch 103 Switch 105 Horizontal selection switch 106 Horizontal sensitivity switch 107 Auto sensitivity switch 114 G type determination switch 115 Check switch 122, 1 3 input interface 125 output interface 130 shrinkage trunnion shaft rotation hydraulic cylinders extend solenoid 131 trunnion shaft rotating hydraulic cylinder solenoid 133 buzzer 135 nonvolatile memory 136 communication device

Claims (2)

In a work vehicle provided with a hydrostatic continuously variable transmission (34) that outputs the power of the engine (5) by adjusting the rotation angle of the trunnion shaft (92),
A trunnion shaft turning hydraulic cylinder (93) for determining a turning angle of the trunnion shaft (92) of the hydrostatic continuously variable transmission (34);
A trunnion shaft position sensor (92a) which is provided between the trunnion shaft (92) and the hydraulic cylinder (93) and detects the rotational angle position of the trunnion shaft (92) by the operation of the hydraulic cylinder (93);
A forward / reverse lever (10) for switching the traveling direction of the vehicle to the longitudinal direction;
When the neutral position set by the forward / reverse lever (10) is set as the neutral target position of the trunnion shaft (92), the neutral reference value is obtained by using the sensor value of the neutral target position by the trunnion shaft position sensor (92a) as a neutral reference value. Operation control of the hydraulic cylinder (93) is performed so that the neutral reference value based on the sensor value becomes the center value of the reciprocating operation of the hydraulic cylinder (93) after reciprocating the range in the vicinity of the vehicle forward and backward a plurality of times. A work vehicle comprising a controller (90) for performing. The control output for operating the hydraulic cylinder (93) of the controller (90) is a pulse output consisting of on-time and off-time,
The controller (90) controls the on-time to be shorter after the sensor value of the trunnion shaft position sensor (92a) reaches the neutral reference value vicinity range than before the neutral reference value vicinity range. Further, after reaching the neutral reference value vicinity range, the short on-time is corrected little by little from the vehicle forward side to the vehicle reverse side or from the vehicle reverse side to the vehicle forward side. The work vehicle according to 1.

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