JP2000225863A - Transmission device for working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently perform a work by adopting a CVT automatically decelerating due to an increase in load and automatically increasing torque before generation of an engine stop. SOLUTION: This device is provided with a hydraulic gear shift control means 1 performing a gear shift operation of a CTV 7 by performing a far and near operation for a movable pulley piece 15b by feed/discharge of pressure oil and an automatic hydraulic deceleration means J in which a gear shift ratio of the CTV 7 is automatically changed to a deceleration side when driving load for an engine exceeds a prescribed value by change and adjustment of a hydraulic set value in this hydraulic gear shift control means 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission for a working machine using a belt continuously variable transmission (hereinafter abbreviated as CVT) as a transmission for a traveling device. TECHNICAL FIELD The present invention relates to a technique for forming a transmission suitable for a working machine by making good use of a characteristic that is gradually decelerated.

[0002]

2. Description of the Related Art As shown in Japanese Patent Application Laid-Open No. 7-329587, a transmission device used for a working machine such as a tractor is equipped with an HST so that a continuously variable shift can be performed with good shifting operability. As disclosed in Japanese Patent Application Laid-Open No. 4-362429, a structure in which a gear transmission with a synchronization mechanism is switched by a hydraulic clutch in order to eliminate a manual clutch operation at the time of a shift operation, that is, a so-called no-clutch shift structure. Are known.

[0003]

Generally, in a working machine such as a tractor or a rice transplanter, a work traveling or a traveling traveling is performed in a state in which an engine speed is set and maintained at a predetermined working speed by operating a hand accelerator lever. The change of the traveling speed is adjusted by operating the transmission. Therefore, for example, during tilling work with a tractor, the field may change to clay or the turning load may increase rapidly when turning on muddy ground, but in the conventional transmission described above, unless the gearshift operation is intentionally performed, However, since the present speed ratio is maintained, the engine speed drops when the running load increases.

[0004] In such a case, the working efficiency is remarkably reduced, and in some cases, there is a possibility that the engine may stall. Therefore, it is desired that the engine can be automatically decelerated before a clear engine drop occurs so that the working can be performed efficiently. I have. In view of the above, the present invention provides a transmission device that does not have the above-described inconvenience by focusing on a CVT that can easily exhibit the property of automatically decelerating due to an increase in traveling load and applying the CVT to a work machine. With the goal.

[0005]

[Means for Solving the Problems] A first aspect of the present invention is a hydraulic transmission device for a working machine, comprising: a hydraulic shift control means for performing a CVT shift operation by supplying and discharging hydraulic oil; and a hydraulic pressure set by the hydraulic shift control means. And a hydraulic automatic deceleration means for automatically changing the speed ratio of the CVT to the deceleration side when the driving load on the engine exceeds a predetermined value by the change adjustment of the engine.
It is characterized in that the predetermined value can be adjusted.

A second invention relates to a transmission for a working machine,
By means of a hydraulic shift control means for performing a shift operation of the CVT by supply and discharge of hydraulic oil, and a change adjustment of a set hydraulic pressure value by the hydraulic shift control means, the gear ratio of the CVT is automatically reduced when the driving load on the engine exceeds a predetermined value. And a hydraulic automatic deceleration means that is changed to a negative side, and increases the predetermined value when the CVT is shifted to the deceleration side, and decreases the predetermined value when the CVT is shifted to the speed increasing side. A predetermined value changing means for linking the means and the automatic hydraulic deceleration means is provided.

According to a third aspect of the present invention, there is provided a transmission for a working machine,
By means of a hydraulic shift control means for performing a shift operation of the CVT by supply and discharge of hydraulic oil, and a change adjustment of a set hydraulic pressure value by the hydraulic shift control means, the gear ratio of the CVT is automatically reduced when the driving load on the engine exceeds a predetermined value. And a hydraulic automatic deceleration means that is changed to the negative side, and the set value is decreased when the belt continuously variable transmission is shifted to the deceleration side, and the set value is increased when the speed is shifted to the increased speed side. And a setting pressure changing means for linking the hydraulic shift control means and the automatic hydraulic deceleration means.

[0008] A fourth invention is the invention according to the second or third invention, wherein:
The predetermined value changing means is configured to operate a pressure control valve for adjusting and setting the supply oil pressure value by moving the movable pulley piece in a distance direction.

The fifth invention is characterized in that, in the second to fourth inventions, an adjusting tool is provided which can arbitrarily change and set the ratio of the change of the predetermined value to the change of the gear ratio in the predetermined value changing means. I do.

A sixth invention relates to a transmission for a working machine,
The drive or driven side pulley in the CVT is configured as a split pulley composed of a fixed pulley piece and a movable pulley piece movable in the axial direction by a hydraulic cylinder with respect to the fixed pulley piece, and a supply position for supplying pressure oil to the hydraulic cylinder; A control valve having a discharge position for draining oil from a hydraulic cylinder and a neutral position between these positions, and a shift lever interlocked to a spool of the control valve via a first spring. And the movable pulley piece are interlockingly connected via a second spring, and the elastic force generated by the expansion and contraction of the first spring due to the operation of the shift lever, and the expansion and contraction of the second spring due to the distance movement of the movable pulley piece due to the operation of the lever And a feedback control means for automatically returning the switched control valve to neutral by canceling with the elastic force generated in the step (1).

A seventh aspect of the present invention relates to a transmission for a working machine,
By means of a hydraulic shift control means for performing a shift operation of the CVT by supply and discharge of hydraulic oil, and a change adjustment of a set hydraulic pressure value by the hydraulic shift control means, the gear ratio of the CVT is automatically reduced when the driving load on the engine exceeds a predetermined value. The automatic hydraulic deceleration means is changed to the side, and when the drive load exceeds a predetermined value, the automatic hydraulic deceleration means operates, and the hydraulic shift control means appears regardless of the drive load. The shift maintaining mode in which the shift state is maintained can be selected and set freely.

[Operation] According to the configuration of the first aspect, the following operation is obtained. In the CVT, a state in which the force of the drive side split pulley that pushes the movable pulley piece closer to the fixed pulley piece exceeds the force that pulls the movable pulley piece away from the fixed pulley piece due to belt tension (first state). In the state, the present speed ratio state is maintained. However, in a state in which the separating force is larger than the pushing force due to the increase in the traveling load (second state), the belt winding radius of the driving pulley is reduced and the speed is reduced. The characteristic is that the driving torque automatically increases.

Therefore, if the CVT shift operation is performed by a hydraulic control system in which hydraulic pressure is supplied and discharged, the pressure can be changed to easily and freely set and change the pressing force of the movable pulley to the fixed pulley. The first state or the second state
It is possible to freely adjust the setting of a predetermined value that determines either of the states.If the predetermined value is set low, a state in which the load is slightly decelerated as soon as the load torque increases is obtained, and if the predetermined value is set high, the load will be reduced. When the torque is greatly increased, a deceleration state can be obtained. Further, by setting the predetermined value to be much higher, it is possible to obtain a state in which the present speed ratio is maintained regardless of the increase in the traveling load.

That is, when the load torque is increased, the work is immediately decelerated (for example, towing or transporting a slope), or when the load torque is increased to some extent, the work is decelerated (for example, plowing work, subsoiler work [grooves such as culverts and culverts, etc.]). Moat work)), etc., and it is possible to set an automatic deceleration state suitable for various work forms, and also to set a state where automatic deceleration is not performed.

According to the configuration of the second aspect, the following operation is provided. The CVT transmits power by friction between the left and right inclined side surfaces of the belt and the pulley surface. However, if the transmission ratio is different, the contact area between the belt and the pulley is different. Therefore, the pressing force required for the movable pulley piece depends on the load torque and the transmission ratio. Change.
For example, assuming that the pressing force of the movable pulley piece on the driven pulley is constant (3000 kgf), as shown in FIG. As the load torque increases, it increases regardless of the gear ratio. The pressing force of the driven pulley 3000 kgf is:
This is an example of a value that does not cause belt slip even at the maximum load torque of 100 kgm in FIG.

In the CVT having the characteristics shown in FIG. 14, the pressing force of the movable pulley piece on the driving pulley is reduced to 35.
When the reduction gear ratio is set to 00 kgf, a load torque of about 35 kgm is balanced at a reduction ratio of 1.0, and a load torque of approximately 73 kgm is balanced at a reduction ratio of 1.5. As shown in FIG. A line a rising upward is drawn. In other words, the present speed ratio is maintained in the area below the line a, but when the load torque increases beyond the line a, the movable pulley moves away from the fixed pulley piece (the second state described above). The gear ratio is automatically changed to the deceleration side along the line a until the pressing force of the movable pulley piece and the force for moving the movable pulley piece away from the fixed pulley piece by the belt tension are balanced.
Therefore, a state in which the area is above the line a does not appear.

Therefore, if the predetermined value is increased when the CVT is decelerated, and the predetermined value is decreased when the CVT is accelerated, the slope of the line a which is naturally determined from the components of the CVT, the set pressure, and the like is calculated as shown in FIG. As shown in a line b indicated by a dashed line, the line can be made steeper to the right. This is to reduce the amount of deceleration when the load torque exceeds a predetermined value, that is, to make the automatic deceleration operation insensitive to an increase in the load torque insensitive. It is suitable for work (for example, plow work, rotary work, and the like) that places more importance on keeping the traveling speed as constant as possible rather than shortage.

On the other hand, in the configuration of claim 3, the CVT
When the deceleration operation is performed, the predetermined value decreases, and when the speed increasing operation is performed, the predetermined value increases. Therefore, the gradient of the line a described above is changed to a line c indicated by a virtual line and a line e indicated by a broken line in FIG.
It can be made loose to the right. This is to increase the amount of deceleration when the load torque exceeds a predetermined value, that is, to make the automatic deceleration operation sensitive to an increase in the load torque, and while requiring the automatic deceleration state,
This is suitable for work (for example, subsoiler work) in which giving a sufficient driving torque is more important than keeping the running speed constant.

According to the fourth aspect of the present invention, the change of the gear ratio in the CVT means the change of the position of the movable pulley in the axial direction. It is possible to easily correspond to the predetermined value which is a pressure balanced with the pressing force acting on the piece and changes according to the speed ratio, and it is not necessary to provide a means for separately detecting a change in the speed ratio. preferable.

According to the configuration of claim 5, as described above, the automatic deceleration operation may be insensitive depending on the work content,
In some cases, it is better to be sensitive, so if the ratio of the change of the predetermined value to the change of the gear ratio in the predetermined value changing means can be adjusted, an automatic deceleration state suitable for various work contents can be set. Work efficiency can be further improved.

According to the configuration of claim 6, as will be described in detail in the embodiment, the movable pulley piece and the shift lever are respectively mounted on the spool of the control valve for moving the movable pulley piece in the axial direction by the hydraulic cylinder. Due to the structure of interlocking connection via a spring, the speed is shifted by the amount by which the shift lever is moved, and the shift position corresponding to the moved lever position is automatically maintained. That is, feedback control for adjusting the gear ratio in accordance with the operation position of the shift lever can be performed by inexpensive mechanical means using the control valve spool.

According to the seventh aspect of the present invention, as in the operation of the first aspect of the present invention, the CVT shift operation is performed by a hydraulic control system in which hydraulic pressure is supplied and discharged. It is possible to easily and freely set and change the pressing force of one piece to the fixed pulley piece. Therefore, the adjustment setting of the predetermined value for determining either the first state or the second state can be realized by a simple modification such as providing a pressure control valve and an artificial adjuster thereof, and the load torque is large. The automatic deceleration mode, which automatically decelerates when the speed changes, and the shift maintaining mode, in which the displayed gear ratio is maintained regardless of the magnitude of the load torque, can be selected and set with a simple structure. Become.

[Effect] In the working machine according to the first aspect, C
A phenomenon in which the gear ratio is automatically changed to a deceleration side with an increase in load torque by shifting the VT by hydraulic control;
Also, it is possible to easily adjust and set how much the load torque increases when the automatic deceleration is performed, and it is possible to set an automatic deceleration state suitable for various operations, thereby providing an excellent transmission device capable of effectively utilizing the characteristics of the CVT. We were able to.

In the working machine according to the second and third aspects,
(A) By changing the speed of the CVT by hydraulic control, the automatic deceleration state in which the gear ratio is automatically changed to the deceleration side with the increase of the load torque is changed to the load torque and the gear ratio when the automatic deceleration is performed. The relationship can be adjusted and set so that it is not unique and can be adapted to various works, and a transmission device that can further improve work efficiency can be provided.

In the working machine according to the fourth aspect, by utilizing the movement of the movable pulley piece, the above-mentioned effect (a) in the transmission using the hydraulically controlled shift operation means can be simplified and reduced in cost. There are advantages that can be done.

In the working machine according to the fifth aspect, the ratio of the change of the set value to the change of the gear ratio in the set pressure changing means can be arbitrarily changed and set, and is suitable for various work contents such as rotary work and plow work. An automatic deceleration state can be set, and a transmission device that functions more efficiently by setting shift characteristics in accordance with various operations is obtained.

In the working machine according to the sixth aspect of the present invention, by utilizing a hydraulic shift control type configuration in which the shift lever and the movable pulley piece are interlockedly linked to the control valve spool, the working lever can be operated in accordance with the operating position of the shift lever. A cost-effective transmission device in which feedback control means excellent in operability capable of adjusting the gear ratio can be achieved by simple and inexpensive mechanical means.

In the working machine according to the present invention, the CVT is shifted by hydraulic control to automatically change the gear ratio to the deceleration side with an increase in load torque. Regardless of this, the means for selecting and setting the shift maintaining mode for maintaining the present gear ratio can be configured simply and inexpensively, and the automatic decelerating state and the constant gear ratio state make it possible to establish a gear state suitable for a wider range of work. Set,
An excellent transmission that can effectively utilize the features of CVT can be provided.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a transmission device of a tractor, which is an example of a working machine. Reference numeral 1 denotes an engine mounted on the front of the body, 2 denotes a monobody structure that is connected to a rear surface of the engine 1 and supports a rear axle 3. Mission case, 4
Is a hydraulic cylinder for lifting and lowering the working device, and 5 is a floor step of the operating unit.

As shown in FIGS. 2 and 3, the transmission case 2 has various gear shifting mechanisms such as a clutch housing portion 2A having a main clutch 6, a first case portion 2B having a CVT 7, and a subtransmission mechanism 13. 2nd case part 2 provided with mechanism
C. The second case portion 2C includes a front case portion 2a including a hydraulic clutch (an example of a speed change clutch) 8 for traveling speed change, a forward / reverse switching mechanism 9, and the like, a super speed reduction mechanism 10 for traveling, and a front wheel speed change mechanism from the front. 11 and an intermediate case portion 2b provided with a differential mechanism 12 and the like.
c.

The driving power is the main clutch 6, the CVT
7, forward / reverse switching mechanism 9, auxiliary transmission mechanism 13, super reduction mechanism 1
0, and can be transmitted to the left and right rear axles 3 and 3 via the differential mechanism 12 and can be transmitted to the front wheel drive shaft 14 via the front wheel transmission mechanism 11 from the auxiliary transmission mechanism 13 having the front-rear rotating shaft 13a. It is also configured. The power for the PTO is generated by the PTO projecting rearward from the differential case portion 2c via the drive pulley shaft 15j of the CVT 7 and the PTO transmission mechanism 16.
It is transmitted to the shaft 17.

As shown in FIGS. 3 to 5, the CVT 7 includes a driving pulley 15 having a split pulley structure having a fixed pulley piece 15a and a movable pulley piece 15b, and a fixed pulley piece 1 similarly.
A wet belt is formed by winding a steel belt 19 over a driven pulley 18 having a split pulley structure including a movable pulley 8a and a movable pulley piece 18b. The drive shaft 15j of the drive pulley 15 and the driven shaft 18j of the driven pulley are both disposed in the front-rear direction at substantially the same height level (the drive shaft 15j is slightly higher), and are disposed on the left and right sides of the first case portion 2B. An input shaft 20 via the main clutch 6 is disposed at a position slightly above the left and right sides of the pulley shafts 15j and 18j.

The traveling-speed hydraulic clutch 8 of the multi-plate friction wet type structure is disposed on a driven shaft 18j which is an output shaft of the CVT 7, and a forward / reverse switching mechanism 9 disposed on the lower side in the transmission direction. Both of the two-stage high and low sub-transmission mechanisms 13 are of a synchronous meshing type (synchronized type). And
As shown in FIGS. 3 and 13, shift rotators 9 g, 9 b of each of the speed change mechanisms 9, 13 based on an electric signal from a speed change operation tool 49 such as a lever or a switch, or an operation command such as a pilot pressure.
Hydraulic cylinders (an example of an actuator) cy1 and cy2 for shifting gears by moving 13 g are externally (or internally) mounted on the transmission case 2 and these hydraulic cylinders cy1 and c
When the shift operation by y2 is started, the shut-off control means 47 for operating the hydraulic clutch 8 to the transmission cut-off side in conjunction with the shift operation.
And transmission control means 48 for operating the hydraulic clutch 8 to the transmission side in conjunction with the end of the shift operation by the hydraulic cylinders cy1 and cy2.

The no-clutch transmission structure in which the hydraulic cylinders cy1, cy2 and the hydraulic clutch 8 are combined has already been disclosed in the latter publication (Japanese Patent Laid-Open No. 4-362429), Japanese Patent Laid-Open No. 9-242858, and the like. Further description of the known technique is omitted. still,
The three-stage PTO transmission mechanism 16 and the super reduction mechanism 10
The shift rotary members 16g and 10g are directly operated by the PTO shift lever 50 and the creep lever 51, respectively.

An inner cylinder 26 made of sheet metal is integrally connected to the movable pulley piece 15b on the driving side which is spline-fitted to the driving shaft 15j, and is connected to an outer cylinder 27 mounted on the driving shaft 15j so as to be axially immovable. A drive-side hydraulic cylinder 28 that can be forcibly moved in a direction in which the movable pulley piece 15b approaches the fixed pulley piece 15a by slidably fitting the inner cylinder 26 is formed. The supply and discharge of the pressure oil to and from the drive side hydraulic cylinder 28 is performed via a movable pulley piece 15b and a supply and discharge oil passage 33 formed inside the drive shaft 15j.

Similarly, an outer cylinder 30 integrally connected to a movable pulley piece 18b that is splined to the driven shaft 18j,
The movable pulley piece 18b is fixed to the fixed pulley piece 18 by fitting the driven shaft 18j with an outer cylinder 31 that is not axially movable.
The driven hydraulic cylinder 29 is configured to be forcibly movable in a direction approaching a. The supply and discharge of pressure oil to and from the driven hydraulic cylinder 29 is performed via a movable pulley piece 18b and a supply / discharge oil passage 34 formed inside the driven shaft 18j. Do it. The driven hydraulic cylinder 29 is provided with a winding spring 32 for urging the movable pulley piece 18b in a direction approaching the fixed pulley piece 18a.

The hydraulic cylinder 4 integrally formed on the upper part of the differential case portion 2c is of a single-acting type in which the lift arm 4a moves upward by supplying hydraulic oil and the lift arm 4a moves downward by draining oil. Drain the oil in the differential case 2c
Alternatively, the oil passage is formed so as to return to the intermediate case portion 2b, that is, the second case portion 2C, and the lubricating oil suction port 22 of the transmission case 2 for the hydraulic pump 21 which is arranged beside the engine 1 and driven by the engine is It is provided below the first case part 2B.

The first case portion 2B and the second case portion 2C are separated from each other, and a large number of holes 23a are formed in a partition wall 23 for supporting a bearing for shaft support. The interior of the transmission case 2 is configured such that the lubricating oil can flow freely, and the interior of the differential case portion 2c and the later-described suction port 22 are in oil passage communication within the transmission case 2. Accordingly, the pressure oil discharged from the hydraulic pump 21 is supplied from the control valve V to the hydraulic cylinder 4 through a supply oil passage 24 such as an external pipe, and the drain oil is discharged to the transmission case 2.
After flowing in the interior from the rear to the front, a circulation path is formed in which the oil returns to the hydraulic pump 21 through a return oil passage 25 such as an external pipe connected to the suction port 22.

Since the driven pulley shaft 18j on which the hydraulic clutch 8 is arranged coaxially is located slightly below the drive pulley shaft 15j, the hydraulic clutch 8 is sufficiently immersed in the oil level L in the transmission case 2. At the same time, each of the pulleys 15 and 18 is also constantly immersed in lubricating oil, so that a good lubrication and cooling function with the belt 19 can be exhibited.

Next, the speed change operation structure of the CVT 7 will be described in detail. As shown in FIGS. 9 to 11, a control valve 35 for controlling the supply and discharge of hydraulic oil to and from the drive-side hydraulic cylinder 28, and a hydraulic pump 3
6 and a variable relief valve 37 for setting line pressure (an example of a pressure control valve according to claim 4) and the like, constitute a shift hydraulic circuit and a shift lever 38 interlocked with a spool 35s of the control valve 35 is provided. Thus, the hydraulic shift control means I is constituted. The control valve 35 has a pump port 35a and a cylinder port 35b that communicates with the drive side oil supply / discharge passage 33.
And a drain port 35c for draining oil toward a shift hold valve (not shown) are formed in this order.

The control valve 35 has a supply position p for supplying pressure oil to the drive side hydraulic cylinder 28 by a spool operation, a discharge position d for discharging oil from the drive side hydraulic cylinder 28, and a neutral position between these positions. There are three positions with n. A shift lever 38 is interlockedly connected to one end of the spool 35s via a first spring 39, and the other end of the spool 35s is connected to a driving side movable pulley piece 15 via a second spring 40, which is the same component as the first spring 39.
b are interlockingly connected with the sliding direction of the spool 35s and the moving direction of the spool 35s aligned.

The first spring 39 accompanying the operation of the shift lever 38
The elastic force generated by the expansion and contraction of the spring and the elastic force generated by the expansion and contraction of the second spring 40 due to the distance movement of the movable pulley piece 15b associated with the lever operation cancels out the feedback that the switched control valve 35 automatically returns to neutral. The control means A is constituted. That is, the spool 35s is provided with both springs 39 and 40.
The biasing force is canceled at the equilibrium position.

The operation of the feedback control means A will be described. First, the shift lever 38 is moved from the neutral position N to the high speed side H.
When i is operated, as shown in FIG. 10, the first spring 39 is extended and the force for pushing the spool 35s toward the second spring 40 is weakened, so that the second spring 40 relatively moves the spool 35s to the first spring 35s.
The pressing force toward the spring 39 increases, and the spool 35s
It moves to the spring 39 side. Then, the control valve 35 is switched to the supply position p, and the pump port 35a and the cylinder port 35b communicate with each other, supply pressure oil to the drive side hydraulic cylinder 28 to move the movable pulley piece 15b closer to the fixed pulley piece 15a. Then, the winding ratio of the belt 19 is forcibly increased to change the speed ratio to the speed increasing side.

The approach movement of the movable pulley piece 15b causes the second spring 40 connected to the rod to be stretched, and the force for pushing the spool 35s toward the first spring 39 is weakened. After the movable pulley piece 15b moves until the pressing urging force with the first spring 39 extended by the operation is balanced, that is, the control valve 35 returns to the neutral position n, the operation is automatically stopped. That is, the speed ratio is changed to the high-speed side by the amount by which the shift lever 38 is moved to the high-speed side, and the speed is increased.

Next, when the shift lever 38 is operated to the low speed Lo side, as shown in FIG. 11, the first spring 39 is compressed to move the spool 35s to the second spring 40 side, and the control valve 35 is moved to the discharge position. d to the drive side hydraulic cylinder 2
Oil is drained from 8. Then, the line pressure and the spring 3 described later
2, the movable pulley piece 18b moves closer to the fixed pulley piece 18a and is operated in a direction in which the winding radius of the belt 19 of the driven pulley 18 becomes larger. The piece 15b moves in a direction away from the fixed pulley piece 15a, and is decelerated.

The deceleration operation moves the movable pulley piece 15b away from the drive side, so that the second spring 40 is compressed and the force pressing the spool 35s against the first spring 39 is increased. The point where the urging force with the first spring 39 is balanced, that is, the control valve 3
After the movable pulley piece 15b moves until the position 5 returns to the neutral position n, it automatically stops. That is, the shift lever 3
The gear ratio is also changed to the low speed side by the amount that the 8 is moved to the low speed side, and the speed is reduced.

The variable relief valve 37 includes a valve body 42, a spool 43 slidable inside the valve body 42, a spring receiving member 44 slidably fitted in the valve body 42, a spool 43 and a spring receiving member. 44 is a compression-type wound spring interposed between
5 and the pump port 35a
A first port 37a communicating with a pump oil passage 41 that communicates with the oil supply / discharge passage 34 on the driven side and a drain port 37b are formed.

The spring receiving member 44 is connected via a connecting member 46 so as to move integrally with the drive-side movable pulley piece 15b, and is positioned by the drive-side movable pulley piece 15b. In FIG. 9, when the spring receiving member 44 is moved to the left (opposite the spool 43 side) by a high-speed operation, as shown in FIG. As a result, the relief pressure, that is, the line pressure is reduced by the throttle action with the drain port 37b slightly opened so that the weakened spring force and the line pressure are balanced.

When the spring receiving member 44 is moved to the right (toward the spool 43) by the low-speed operation of the shift lever 38, the force of pressing the spool 43 of the winding spring 45 is increased by the compressed amount, and as a result, the relief pressure is increased. That is, the line pressure increases. However, it goes without saying that deceleration from the lowest speed state where the reduction ratio is the maximum is impossible.

The line pressure is such that the movable pulley piece 18b on the driven side is constantly pressed and urged toward the fixed pulley piece 18a in cooperation with the spring 32, whereby the tension function of the belt 19 and the pressure are released. If the control becomes impossible, a fail-safe function in which the gear ratio is automatically operated to the deceleration side is exhibited.

That is, due to the connection between the driving-side movable pulley piece 15b and the spring receiving member 44, the line pressure decreases when the speed ratio is changed to the speed increasing side, and the line pressure decreases when the speed ratio is changed to the speed reducing side. It is controlled to rise. Specifically, as shown in the graph of FIG.
When the speed is 5 (double speed), the line pressure is 16 kgf / cm ² , when the reduction ratio is the maximum of 2.5, the line pressure is 28 kgf / cm ² , and the line pressure changes linearly at the reduction ratio between them. .

When the running load increases and the belt tension exceeds a certain value by the automatic change control of the line pressure, the movable pulley piece 1
The force that spreads 5b exceeds the pressing force of the drive side hydraulic cylinder 28 due to the line pressure, and the movable pulley piece 15b moves in a direction away from the fixed pulley piece 15a, and functions to automatically reduce the speed and increase the torque. . That is, when the traveling load such as turning in a wet field is significantly increased, the CVT 7 is automatically decelerated, and problems such as insufficient driving force and engine stall are avoided.

FIG. 6 shows the PTO in the front case 2a.
A portion of a first support wall 59 (a portion indicated by arrows BB) disposed between the speed change mechanism 16 and the forward / reverse switching mechanism 9 is shown. The first support wall 59 forms the forward / reverse switching mechanism 9. A pair of transmission shafts 9a and 9b, and a transmission shaft 13a of the auxiliary transmission mechanism 13;
And is attached to the inward rib portion of the front case portion 2a by bolting.

FIG. 7 shows a shaft arrangement structure at a portion (a portion taken along the line CC) of the intermediate case portion 2b as viewed from the front end of the differential case portion 2c. Reference numeral 16j denotes a PTO input shaft directly connected to the drive pulley shaft 15j. Yes, 16a is a PTO transmission shaft,
b is a PTO reverse rotation axis. FIG. 8 shows the front case part 2.
(a) shows the portion (the arrow DD portion) of the second support wall 60 portion bolted to the rear end portion as viewed from the intermediate case portion 2b;
A pair of transmission shafts 10a, 10 constituting the super reduction mechanism 10
b, the drive shaft 11a of the front wheel transmission mechanism 11, the driven shaft 11b directly connected to the front wheel drive shaft 14, and the like are supported by bearings.

[Another Embodiment] As shown in FIG. 16, the connecting member 46 connected to the movable pulley piece 15b on the driving side and the relief valve 37 are connected in the opposite direction to FIG. The hydraulic shift control means I and the hydraulic automatic deceleration means J are configured to decrease the set value when the CVT 7 is shifted to the deceleration side and increase the set value when the CVT 7 is shifted to the speed increase side. The associated set pressure changing means M "can be configured.

As shown in FIG. 17, the connecting member 46 and the spool 44 of the relief valve 37 are linked by a balance swinging link 65 which can swing at a fulcrum X.
The position of the relief valve 37 connected to the pin 4 by a pin can be adjusted by an actuator such as an electric cylinder 66.
The ratio of the change of the set value to the change of the gear ratio at
An adjustment mechanism 64 "that can be arbitrarily changed and set can be configured.

As shown by imaginary lines in FIGS. 9 to 11, a selection valve 69 is provided to switch between an oil path 67 to the relief valve 37 and a communication with the relief valve 37 or a second relief valve 68. The selection valve 69 can be switched by a switch 71 (a switch between an automatic deceleration mode r and a shift maintaining mode s) via a drive circuit 70, whereby
According to claim 7, "the automatic deceleration mode in which the hydraulic automatic deceleration means J operates when the driving load exceeds a predetermined value, and the shift state appearing by the hydraulic shift control means I irrespective of the driving load. The shift maintaining mode to be maintained can be selected and set freely. "

That is, when the selection valve 69 is switched to the position f, the above-described automatic deceleration mode in which the line pressure is controlled by the relief valve 37 appears, and when the selection valve 69 is switched to the position g, the high pressure for circuit protection is obtained. Second relief valve 68 set to
Since the delivery pump oil passage 41 is controlled, the pressing force of the driving pulley 15 due to the hydraulic pressure of the movable pulley 15b always exceeds the driving load, and a shift maintaining mode in which automatic deceleration is not performed appears.

[Brief description of the drawings]

FIG. 1 is a side view of a tractor.

FIG. 2 is a partially cutaway side view of a transmission case.

FIG. 3 is a diagram showing a transmission structure in a transmission case.

FIG. 4 is a cross-sectional plan view of a transmission case in a CVT portion.

FIG. 5 is a sectional view taken along line AA in FIG. 2;

FIG. 6 is a sectional view taken along line BB in FIG. 2;

FIG. 7 is a sectional view taken along line CC in FIG. 2;

FIG. 8 is a sectional view taken along line DD in FIG. 2;

FIG. 9 is a system diagram showing a shift operation structure of a CVT.

FIG. 10 is a system diagram showing a shift operation structure of the CVT when operated at high speed.

FIG. 11 is a system diagram showing a shift operation structure of a CVT when a low-speed operation is performed.

FIG. 12 is a diagram showing a relationship graph between a gear ratio of a CVT and a line pressure.

FIG. 13 is a block diagram showing a structure of a no-clutch shift control.

FIG. 14 is a table showing a pressing force of a driving pulley determined by a gear ratio and a load torque.

FIG. 15 is a view showing various relational graphs between a gear ratio and a load torque in an automatic deceleration state.

FIG. 16 is a principle diagram showing another structure of the set pressure changing means.

FIG. 17 is a principle view showing another structure of the adjusting mechanism.

[Explanation of symbols]

 Reference Signs List 1 engine 7 CVT 15 split pulley 15a fixed pulley piece 15b movable pulley piece 28 hydraulic cylinder 35 control valve 35s spool 37 pressure control valve 38 shift lever 39 first spring 40 second spring 64 adjustment mechanism A feedback control means I hydraulic shift control means J Automatic hydraulic deceleration means K, M Set pressure change means p Supply position n Neutral position d Discharge position

Claims (7)

[Claims] When a driving load on an engine exceeds a predetermined value, a hydraulic shift control means for performing a shift operation of a belt continuously variable transmission by supply and discharge of hydraulic oil and a change and adjustment of a hydraulic set value by the hydraulic shift control means. A power transmitting device for a working machine, comprising: a hydraulic automatic deceleration means for automatically changing a speed ratio of the belt continuously variable transmission to a deceleration side; and wherein the set value is adjustable. 2. A hydraulic shift control means for performing a shift operation of a belt continuously variable transmission by supply and discharge of hydraulic oil, and a change and adjustment of a hydraulic set value by the hydraulic shift control means, when a drive load on the engine exceeds a predetermined value. A hydraulic automatic deceleration means for automatically changing the speed ratio of the belt continuously variable transmission to the reduction side, and increasing the set value when the belt continuously variable transmission is shifted to the reduction side; A power transmitting device for a working machine, comprising: a set pressure changing unit that links the hydraulic shift control unit and the automatic hydraulic deceleration unit so that the set value is reduced when the speed change operation is performed on the speed increasing side. 3. A hydraulic shift control means for performing a shift operation of a belt continuously variable transmission by supply and discharge of hydraulic oil, and a change and adjustment of a hydraulic set value by the hydraulic shift control means, when a driving load on the engine exceeds a predetermined value. A hydraulic automatic deceleration means for automatically changing the speed ratio of the belt continuously variable transmission to the reduction side, and reducing the set value when the belt continuously variable transmission is shifted to the reduction side; A power transmitting device for a working machine, comprising: a set pressure changing unit that links the hydraulic shift control unit and the automatic hydraulic deceleration unit so that the set value is increased when a shift operation is performed on the speed increasing side. 4. The work according to claim 2, wherein the set pressure changing means is configured to operate a pressure control valve for adjusting and setting a supply pressure of the hydraulic oil by moving the movable pulley piece in a distance direction. Transmission of the machine. 5. The work according to claim 2, further comprising an adjustment mechanism capable of arbitrarily changing and setting a ratio of a change of a set value to a change of a gear ratio in the set pressure changing means. Transmission of the machine. 6. A split pulley comprising a fixed pulley piece and a movable pulley piece which is movable in the axial direction by a hydraulic cylinder with respect to the fixed pulley piece in the belt continuously variable transmission. A control valve having a supply position for supplying pressure oil to the cylinder, a discharge position for discharging oil from the hydraulic cylinder, and a neutral position between these positions, and a spool of the control valve via a first spring. An interlockingly connected shift lever, wherein the spool and the movable pulley piece are interlockedly connected via a second spring, and an elastic force generated by expansion and contraction of the first spring accompanying operation of the shift lever; A feedback control mechanism in which the switched control valve automatically returns to neutral by canceling the elastic force generated by the expansion and contraction of the second spring due to the distance movement of the movable pulley piece accompanying the operation. Working machine of the transmission that is equipped with. 7. A hydraulic shift control means for performing a shift operation of the belt continuously variable transmission by supply and discharge of hydraulic oil, and a change and adjustment of a set hydraulic value by the hydraulic shift control means, when a driving load on the engine exceeds a predetermined value. An automatic deceleration mode in which the gear ratio of the belt continuously variable transmission is automatically changed to a deceleration side, and the hydraulic automatic deceleration means operates when the driving load exceeds a predetermined value; A transmission device for a working machine, wherein a transmission maintaining mode in which a transmission state displayed by the hydraulic transmission control means is maintained irrespective of the driving load can be selectively set.