JP2806461B2 - Travel transmission structure of work vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling power transmission structure for a working vehicle having a pair of left and right traveling devices of a crawler type or a multi-wheel type.

[0002]

2. Description of the Related Art As an example of the work vehicle described above, there is a combine equipped with a pair of right and left crawler type traveling devices. Such a combine is provided with a slow turning clutch capable of transmitting forward rotation power at a speed lower than that of the selected one traveling device and a reverse clutch capable of transmitting reverse rotation power to the selected one traveling device. There are things that are. This makes it possible to surely make a gentle turn even on soft ground by driving one of the traveling devices at low speed. Can turn.

[0003] The above-mentioned selection switching operation between the gentle turning and the super pivot turning is performed by switching the supply direction of hydraulic oil for entering operation to the gentle turning and the reverse rotation clutch by a switching valve, and this hydraulic oil is switched to the gentle turning clutch. Or to the reverse clutch. In this case, a common step-up adjustment mechanism is provided for the gentle turning and reverse rotation clutches, and the operation lever is operated to increase the pressure of the hydraulic oil for the on-going operation to gradually turn and reverse rotation. Operate the clutch. Then, by adjusting the pressure of the hydraulic oil for the on-coming operation by the operation lever and the pressure-increasing mechanism, the on-off state of the gentle turning and the reverse rotation clutch is adjusted to change and adjust the turning radius of the gentle turning or the super turning.

[0004]

[0006] Since super turning with a reverse clutch can be turned with a very small radius,
If a super turning is performed as it is while traveling straight, the aircraft may be swung. Therefore, the spin turn is often performed after stopping once or while traveling at a low speed. Accordingly, if the pressure increase by the pressure increase adjustment mechanism is set so as to be linearly increased from the set low pressure (the pressure at which the reverse clutch is in the transmission cutoff state) in accordance with the operation position of the operation lever, the set low pressure It is easy to finely and slowly adjust the turning radius of the swivel turn while sliding the reverse clutch by changing the pressure little by little by the operating lever in the vicinity.

On the other hand, since a gentle turning using a gentle turning clutch has a large turning radius, even when the vehicle is running on a work site having a low running resistance such as a pavement road, the gentle turning is particularly required. Although there is no problem, since the running resistance is large when working in a field such as a field where the combine is running, the following problems occur when running at a low speed on a working ground where such running resistance is large. May occur. In other words, if the step-up characteristic of the step-up adjustment mechanism is set so as to increase linearly from the set low pressure in accordance with the characteristics of the reverse rotation clutch, the operation lever will be used to turn on the gentle rotation clutch to perform gentle rotation when traveling straight. In this case, if the operation amount of the operation lever is not sufficient, the pressure of the gentle turning clutch is not sufficient, and the traveling device on the turning center side (slow turning clutch side) may stop due to a large running resistance. Therefore, even if the user tries to smoothly make a gentle turn from the straight traveling state, the traveling device on the turning center side stops when the operation lever is slightly operated, and the aircraft turns with an unexpected small radius. SUMMARY OF THE INVENTION It is an object of the present invention to provide a structure in which a gentle turning can be smoothly performed at the same time as a function of finely adjusting a turning radius at a time of a pivot turn and a gentle turning.

[0006]

[A]

Hydraulic slow-turn clutch capable of transmitting forward rotation power at a lower speed than the other traveling device to one of the traveling devices, and reverse rotation power to the selected one of the traveling devices Hydraulic reversing clutch. [B] A switching valve that can be switched between a state in which the operation oil is supplied to the operation of the slow rotation clutch and a state in which the operation oil is supplied to the operation of the reverse rotation clutch. Boost control mechanism. (C) The operation lever and the pressure-increasing mechanism are adjusted so that the pressure for entering the gentle turning clutch or the reverse rotation clutch is increased by the pressure-increasing adjustment mechanism in accordance with the operation position of the operation lever that is manually operated. Linking means for linking, and initial pressure changing means capable of changing the initial pressure of the boosting adjustment mechanism corresponding to the neutral position of the operation lever. [D] Based on the detecting means for detecting the shift position of the transmission for traveling, when the transmission is operated to the lower speed side, the operation of the initial pressure changing means is permitted, and the transmission is operated to the higher speed side. And a check means for preventing the operation of the initial pressure changing means and setting the initial pressure of the boosting adjustment mechanism at the neutral position of the operation lever to a value at which the slow turning clutch and the reverse rotation clutch are in the transmission cutoff state.

[0007]

According to the present invention, when the switching valve is operated on the supply side of the operating oil to the reverse rotation clutch (in the state of turning over the pivot), the initial pressure changing means lowers the initial pressure of the step-up adjusting mechanism. Just set it. As a result, as the operation lever is operated from the neutral position, the pressure of the reverse clutch gradually increases linearly from a low pressure as a linear function.
The turning radius can be finely adjusted in the pivot turn while the reverse clutch is half-clutched and slipped. Then, the switching valve is set on the supply side of the hydraulic oil to the gentle turning clutch (slow turning state).
In the case where the vehicle is operated on a work site having a small running resistance such as a dry field or a pavement road, the initial pressure of the boosting adjustment mechanism may be set low by the initial pressure changing means as described above. . As a result, as the operating lever is operated from the neutral position, the pressure of the gentle turning clutch is gradually increased in a linear function from a low pressure. Fine adjustment of turning radius can be performed.

When the switching valve is operated on the supply side of the hydraulic oil to the gentle turning clutch (slow turning state), when traveling on a work site having a large running resistance such as a wetland or a soft ground, an initial operation is required. What is necessary is just to set the initial pressure of the boosting adjustment mechanism high by the pressure changing means. As a result, when the operation lever is operated from the neutral position, the pressure of the gentle turning clutch increases from the above-described high initial pressure. It quickly reaches the pressure at which the swing clutch is in full transmission. Therefore, if the operation lever is operated from the neutral position while traveling straight, the slow turning clutch is quickly transmitted, and one of the traveling devices is quickly driven at a low speed, so that the smooth turning can be performed.

As described above, when traveling on a work area with a small running resistance (a state in which the turning radius can be finely adjusted in a gentle turning), the work is generally performed at a low speed or when the vehicle is driven at a high speed. is there. Conversely, when traveling on a work site having a large traveling resistance (a state in which the gentle turning clutch is quickly in the transmission state), the vehicle generally travels only at a low speed in many cases. Accordingly, in the present invention, when the traveling transmission is operated to the low speed side, the operation of the initial pressure changing means is permitted, and the initial pressure changing operation can be performed according to the state of the traveling resistance at the work place. As a result, fine adjustment of the turning radius in gentle turning and transition to smooth gentle turning can be performed. On the other hand, when the traveling transmission is operated on the high speed side, the initial pressure cannot be changed, and the pressure of the gentle turning and the reverse clutch is gradually increased from a low pressure as a linear function. Only. Therefore, when the operation lever is operated while the vehicle is traveling straight at high speed,
A state in which the gentle turning or reverse rotation clutch suddenly enters the transmission state and the body suddenly starts turning does not occur.

[0010]

As described above, by changing the initial pressure of the boost control mechanism, the fine adjustment function of the turning radius at the time of turning on the corner and at the gentle turn is left in the boost control mechanism, and especially the running resistance is improved. In a large work area, the boost control mechanism can quickly operate the slow turning clutch to the transmission state to smoothly shift to the slow turning, thereby improving the traveling and turning performance of the work vehicle. In the high-speed running state, a state in which the slow turning or the reverse rotation clutch suddenly becomes the transmission state at the start of turning and the aircraft suddenly starts turning can be prevented, thereby improving safety. Was completed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a structure in a transmission case 8 of a traveling system of a combine as an example of a work vehicle, in which power from an engine (not shown) is transmitted via a belt transmission mechanism (not shown) having a tension clutch. The power is transmitted to the input pulley 2 of the hydrostatic continuously variable transmission 1 and the power from the output shaft 3 of the hydrostatic continuously variable transmission 1 is transmitted to the first transmission shaft 4.
Is transmitted to a reaper (not shown) at the front of the machine.

The power from the first transmission shaft 4 is transmitted to the second transmission shaft 11 via the first gear 9 and the second gear 10.
A shift gear 14 is slidably fitted on the second transmission shaft 11 in a spline structure, and a high-speed gear 16, a medium-speed gear 17, and a low-speed gear 6 are fixed to the third transmission shaft 15. . With the above structure, the shift gear 14 is slid and engaged with the high-speed gear 7, the medium-speed gear 17 or the low-speed gear 6 that meshes with the high-speed gear 16, thereby shifting the forward rotation power for straight traveling into three stages of high, medium and low. This forward rotation power can be applied to the first
The power is transmitted to the transmission gear 19. As described above, the gearshift type transmission 13 (corresponding to a traveling transmission) is constituted by the shift gear 14, the high-speed gear 7, and the like.

A right side gear 21R and a left side gear 21L are rotatably fitted on a support shaft 20 for supporting the first transmission gear 19, and input gears 23 of left and right axles 22 are connected to the left and right side gears 21R, 21R. 21L is always engaged. Thereby, the right or left side gear 21R, 2R
1L is slid with respect to the first transmission gear 19 to engage and disengage, thereby performing power transmission and transmission cutoff operations to the crawler type traveling device 24.
And the left and right side gears 21R, 21L form side clutches 25R, 25L.

Next, a structure for driving one of the traveling devices 24 in the reverse direction will be described. As shown in FIG. 2, a third gear 37 meshing with the high-speed gear 16 of the third transmission shaft 15 is fitted to the fourth transmission shaft 27 so as to be relatively rotatable, and the third gear 37 and the fourth gear
A reverse clutch 30 is provided between the transmission shaft 27 and the transmission shaft 27. A second transmission gear 26 is provided at both left and right ends of the support shaft 20.
R and 26L are supported by bearings, and the fourth transmission shaft 2
Each of the fourth transmission gears 29 fixed to both ends of the
It is in mesh with the transmission gears 26R, 26L.

Thus, the right side gear 21R or the left side gear 21L is connected to the right or left second transmission gear 26.
When the reverse clutch 30 is engaged with the gears engaged with R and 26L, the power from the high-speed gear 16 is transmitted to one of the traveling devices 24 in the reverse rotation state and reduced by half. This is a super-spinning state.

Next, a description will be given of a structure in which one of the traveling devices 24 is driven to rotate forward at a lower speed than the other. As shown in FIG. 2, a small-diameter output gear 38 is mounted on the boss of the first transmission gear 19.
Is fixed, and the third transmission gear 40 having a large diameter is attached to the fourth transmission shaft 27.
Are rotatably fitted to the outside, and the third transmission gear 40 is engaged with the output gear 38. The gentle turning clutch 12 is provided between the third transmission gear 40 and the fourth transmission shaft 27.

As a result, the right or left side gear 21
When the gentle turning clutch 12 is engaged with the R and 21L engaged with the right or left second transmission gears 26R and 26L, the straight forward power transmitted to the first transmission gear 19 is output to the output gear 38. , The third transmission gear 40, the gentle turning clutch 12, the fourth transmission shaft 27, the fourth transmission gear 29, and the right or left second transmission gear 26R, 26L as one of sufficiently reduced forward rotation power. It is transmitted to the traveling device 24. This is a gentle turning state.

Next, a structure for supplying hydraulic oil to the hydraulic cylinders 31R, 31L for performing the sliding operation of the left and right side gears 21R, 21L and the gentle rotation and reverse rotation clutches 12, 30 will be described. As shown in FIG. 1, the hydraulic oil from the pump 32 is supplied to the left and right side gears 21 through the first switching valve 33.
Oil passages 34 are supplied to hydraulic cylinders 31R, 31L for R, 21L, and an oil passage 34 from the side surface of hydraulic cylinders 31R, 31L serves as a second switching valve 35 (corresponding to a switching valve) for gentle turning and reverse rotation clutches 12, 30. It is connected. The oil passage 34 further includes a gentle turning and reverse rotation clutch 1.
A variable relief valve 36 (corresponding to a pressure-up adjusting mechanism) for each of the valves 2 and 30 is connected.

Next, the operation of the first switching valve 33, the second switching valve 35, and the variable relief valve 36 will be described. As shown in FIG. 1, a switching lever 18 operable at three positions is provided on a control unit of the body, and a signal from a limit switch 28 for detecting the operating position of the switching lever 18 is input to the control device 5. I have. The second switching valve 35 is of an electromagnetically operated type, and when the switching lever 18 is operated to the gentle turning position (dry field) and the gentle turning position (wet field), the control device 5 causes the second switching valve 35 to operate the gentle turning clutch 12. When the switch lever 18 is operated to the super pivot position to supply the oil and the switching lever 18 is operated to the super pivot position, the second switching valve 35 is switched to the super pivot position 35b to supply the operating oil to the reverse clutch 30. You.

In the variable relief valve 36, a balance arm 44 operable to increase the spring force (which determines the relief pressure of the variable relief valve 36) for urging the variable relief valve 36 toward the closing side.
(Corresponding to the linking means), and the operation lever 39 provided on the control section of the fuselage and the balance arm 44 are linked by a wire 42 (corresponding to the linking means). Then, the operation lever 39 and the first switching valve 33 are connected to the link mechanism 4.
1 are mechanically linked.

With the above structure, when traveling on a place where running resistance is small, such as a dry field or a pavement road, the switching lever 18 is operated to a gentle turning position (dry field) or a super turning position. As shown in FIG. 1, it is assumed that the switching lever is operated to the gentle turning position (dry field) and the second switching valve 35 is operated to the gentle turning position 35a. In this state, the operation lever 39 is moved to the neutral position N.
, The first switch 33 is also operated to the neutral position, the left and right hydraulic cylinders 31R, 31L are contracted, and the left and right side gears 21R, 21L are engaged with the first transmission gear 19. Accordingly, the forward rotation power transmitted to the first transmission gear 19 is transmitted to the left and right traveling devices 24, and the left and right traveling devices 24 are driven at the same speed, so that the aircraft goes straight.

Next, when the operating lever 39 is operated from the neutral position N to the first turning position R1 on the right or the first turning position L1 on the left, only the first switching valve 33 is operated, and the hydraulic cylinder 3 is operated.
The right or left operation unit 46R, 46R can be operated by 1R or 31L.
Through L, the right or left side gear 21R, 21L that has engaged with the first transmission gear 19 separates from the first transmission gear 19 and engages with the right or left second transmission gear 26R, 26L.

In this case, as shown in FIGS. 1 and 3, the variable relief valve 36 is in the fully opened state,
Has become the set low pressure, and the gentle turning clutch 12 is in the transmission cutoff state. As a result, the transmission to the right or left traveling device 24 is interrupted (the side clutch 25R).
Or the 25 L transmission cutoff state), and the aircraft gradually turns right or left. The sequence valve 47 provided in the oil passage 34 is configured such that the right or left side gear 21R, 21L is connected to the right or left second transmission gear 26R, 2R.
This is for securing the pressure necessary for completely engaging the 6L with the hydraulic cylinders 31R and 31L.

Next, the operating lever 39 is moved from the right or left first turning position R1, L1 to the right or left second turning position R2, L1.
2, the second switching valve 35 is moved to the gentle turning position 35.
In the state of operation a, the wire 42 shown in FIG. 1 is pulled toward the operation lever 39, and the spring force of the variable relief valve 36 is increased by the balance arm 44.

As a result, as shown by the solid line A1 in FIG. 3, the relief pressure of the variable relief valve 36 (the pressure of the gentle turning clutch 12) is increased in accordance with the operating position of the operating lever 39, and the gentle turning clutch 12 is engaged. Going operated. As a result, the slow turning clutch 12 starts to operate, and the right or left traveling device 24 is gradually driven forward at a low speed, and the aircraft slowly turns right or left. And operation lever 3
At the right or left second turning position R2, L2 of No. 9, the gentle turning speed becomes maximum.

Next, it is assumed that the switching lever 18 is operated to the super pivot position and the second switching valve 35 is operated to the super pivot position 35b. In this state, the operation lever 39 is moved to the neutral position N.
When the operating lever 39 is operated from the neutral position N to the right or left first turning position R1 or L1, the right or left side clutch is operated in the same manner as described above. The transmission cutoff state of 25R, 25L appears.

Next, the operating lever 39 is moved from the right or left first turning position R1, L1 to the right or left second turning position R2, L1.
2, the wire 42 shown in FIG. 1 is pulled toward the operation lever 39 and the balance arm 44 is operated in a state where the second switching valve 35 is operated to the super pivot position 35b as described above. Accordingly, the spring force of the variable relief valve 36 is increased.

As a result, as shown by the solid line A1 in FIG. 3, the relief pressure of the variable relief valve 36 (the pressure of the reverse clutch 30) is increased according to the operating position of the operating lever 39, and the reverse clutch 30 is engaged. Go. As a result, the reverse rotation clutch 30 starts to operate, and the right or left traveling device 24 is gradually driven to rotate in the reverse direction, and the airframe makes a right or left turn. Then, at the right or left second turning position R2, L2 of the operation lever 39, the reverse rotation speed becomes maximum.

Next, when traveling on a place where traveling resistance is large, such as a soft field with a lot of water or a weak unpaved road, the switching lever 18 is operated to a gentle turning position (wetland), and The 2 switching valve 35 is operated to the gentle turning position 35a. FIG.
As shown in the figure, the balance arm 44 for the variable relief valve 36
Is provided with a solenoid 45 (corresponding to an initial pressure changing means) which can be pressed and pushed to a position where the spring force of the variable relief valve 36 is maximized. Thereby, the switching lever 1
When the controller 8 is operated to the gentle turning position (wet field), the controller 5 operates the solenoid 45 to the extension side based on the signal of the limit switch 28. Therefore, the balance arm 44 is swung, the spring force of the variable relief valve 36 is set to the strongest state (the state in which the relief pressure of the variable relief valve 36 is the highest), and the gentle turning clutch 12 is already in the complete transmission state. It has become.

Thus, if the operating lever 39 is operated to the neutral position N in this state, the first switching valve 33 is also operated to the neutral position as described above, and the left and right side gears 21R,
21L engages with the first transmission gear 19, and the first transmission gear 1
9 is transmitted to the left and right traveling devices 24, the left and right traveling devices 24 are driven at the same speed, and the aircraft goes straight.

When the operating lever 39 is operated from the neutral position N to the first turning position R1 on the right or the first turning position L1 on the left, only the first switching valve 33 is operated in the same manner as described above, and the hydraulic cylinder 31R or By 31L, the right or left side gear 21R, 21L is separated from the first transmission gear 19 and meshes with the right or left second transmission gear 26R, 26L. In this case, as shown by the dashed line A2 in FIG.
5 and the balance arm 44, the gentle turning clutch 12 is already in a complete transmission state, so that the right or left side gear 21R, 21L is changed to the right or left second transmission gear 26R, 2
When the vehicle engages with the 6L, the forward rotation power at a low speed (a state in which the gentle turning speed is the maximum) is transmitted from the gentle turning clutch 12 to the right or left traveling device 24, and the aircraft slowly turns right or left. . Then, even if the operation lever 39 is operated to the right or left second turning position R2, L2, the same state is maintained.

As shown in FIG. 1, the transmission 13 for traveling
A shift lever 43 (see FIG. 2) is provided in the control section of the fuselage, and a limit switch 48 (corresponding to detection means) for detecting that the shift lever 43 is operated to the low speed position. . With the above structure, when the shift lever 18 is operated to the gentle turning position (wet pad) while the shift lever 43 is operated to the low speed position as shown in FIG. 1, the solenoid 45 is extended, and the solenoid 45 in FIG. Slow turning can be performed with the characteristics shown by the one-dot chain line A2. When the switching lever 18 is operated to the gentle turning position (dry field), the solenoid 4
5 does not perform the extension operation, and can perform gentle turning with the characteristics as indicated by the solid line A1 in FIG. When the shift lever 43 is operated to the low speed position and the switching lever 18 is operated to the super pivot position, the super reverse pivot can be performed by the reverse rotation clutch 30 with the characteristic as shown by the solid line A1 in FIG. It is.

When the shift lever 43 is operated to the middle speed position or the high speed position, the solenoid 45 is extended even if the switching lever 18 is operated to the gentle turning position (wet paddy) or the super turning position. The second switching valve 3
No. 5 is not operated to the super pivot position 35b. Accordingly, in a state where the shift lever 43 is operated to the middle speed position or the high speed position, a state where the switch lever 18 is operated to the gentle turning position (dry rice field) is set regardless of the operation position of the switch lever 18 and is always set. A gentle turn having a characteristic as indicated by the solid line A1 in FIG. 3 is performed (the above corresponds to the restraint means).

[Another Embodiment] In the embodiment shown in FIG.
In this type, two states, ie, the state of the characteristic and the state of the dash-dot line A2, are selectively switched, this may be configured as shown in FIG. As shown in FIG. 4, the variable relief valve 3
A linkage rod 53 operable to push the balance arm 44 for 6 toward the side where the spring force is strengthened by abutment, and a change lever 49 (corresponding to an initial pressure changing means) for pushing and pulling the linkage rod 53 are provided. A friction holding mechanism 50 capable of holding the lever 49 at an arbitrary position is provided. As a result, if the change lever 49 is operated to the low position, a gentle turning with the characteristics as indicated by the solid line A1 in FIG. 5 can be performed. And the change lever 49
Can be changed to an arbitrary position and the balance arm 44 is pressed and pressed, whereby the initial pressure of the gentle turning clutch 12 can be arbitrarily changed as shown by dashed lines A3 and A4 in FIG. In the configuration of FIG. 4, the operation by the change lever 49 is possible only when the shift lever 43 is operated to the low speed position, and when the shift lever 43 is operated to the middle speed position or the high speed position, the change lever is operated by the actuator 54. 4
9 is returned to the low position to return to a gentle turning state having characteristics as indicated by the solid line A1 in FIG.

In this combine, as shown in FIG. 6, in a crawler type traveling device 24, traveling wheels 51 are fixed to driving sprockets 24a of the left and right traveling devices 24, and caster wheels 52 are provided at the rear of the body. Is also possible. By providing the configuration shown in FIG. 1 or FIG. 4 in this state, high-speed traveling is possible while performing gentle turning with characteristics as indicated by the solid line A1 in FIG. 3 or FIG.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a first switching valve and a hydraulic cylinder for left and right side gears, a second switching valve for a gentle turning and reverse rotation clutch, a variable relief valve, and the like.

FIG. 2 is a schematic diagram showing a transmission structure of a traveling system in a transmission case.

FIG. 3 is a diagram showing a relationship between pressure of a gentle turning and reverse rotation clutch and an operation position of an operation lever.

FIG. 4 is a hydraulic circuit diagram showing a first switching valve and a hydraulic cylinder for left and right side gears, a second switching valve for a gentle turning and reverse rotation clutch, a variable relief valve, and the like in a first alternative embodiment.

FIG. 5 is a diagram showing the relationship between the pressure of a gentle turning and reverse clutch and the operating position of an operating lever in a first alternative embodiment.

FIG. 6 is an overall side view of a combine according to a second alternative embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Slow turning clutch 13 Traveling transmission 24 Traveling device 30 Reverse clutch 35 Switching valve 36 Boost adjustment mechanism 39 Operating lever 42,44 Linking means 45,49 Initial pressure changing means 48 Detecting means N Neutral position of operating lever

Continuation of the front page (56) References JP-A-2-267081 (JP, A) JP-A-58-30872 (JP, A) JP-A-55-152914 (JP, U) JP-A-3-61478 (JP) , U) Hikaru 3-129570 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) B62D 11/04-11/08

Claims (1)

(57) [Claims] 1. A traveling power transmission structure for a work vehicle including a pair of left and right traveling devices (24), the traveling power transmission structure for a work vehicle having the following configurations (A) to (D). [A] A hydraulic slow turning clutch (12) capable of transmitting forward rotation power at a lower speed than the other traveling device (24) to one of the traveling devices (24), and the traveling device (2
4) A hydraulic reverse clutch (30) capable of transmitting reverse power to one of the selected ones. [B] A switching valve (35) that can be switched between a state in which the operation oil is supplied by entering the gentle rotation clutch (12) and an operation oil is supplied by entering the reverse rotation clutch (30).
And the slow turning clutch (12) and the reverse rotation clutch (3).
Common boost control mechanism (36) for 0). [C] In accordance with the operation position of the operation lever (39) that is manually operated, the pressure for entering the gentle turning clutch (12) or the reverse rotation clutch (30) is increased by the pressure increasing adjustment mechanism (36). Said operating lever (39) to be operated
Linking means (4) for linking the pressure control mechanism (36)
2), (44) and initial pressure changing means (45), (49) capable of changing the initial pressure of the boosting adjustment mechanism (36) corresponding to the neutral position (N) of the operation lever (39). . [D] Based on the detecting means (48) for detecting the shift position of the traveling transmission (13), if the transmission (13) is operated to the lower speed side, the initial pressure changing means (45), (4
9), the initial pressure changing means (45), (49) when the transmission (13) is operated to the high speed side.
The initial pressure of the booster adjusting mechanism (36) in the neutral position (N) of the operating lever as well as preventing the operation of (39)
The Yuru旋 times clutch (12) and reverse clutch (30)
Checking means to set to a value at which the transmission is cut off .