JPH0510440A - Transmission gear for tractor - Google Patents

Abstract

PURPOSE:To improve the disposition freedom of a shuttle speed change lever and an auxiliary speed change lever by providing a hydraulic clutch oil passage cutoff change-over valve and a hydraulic cylinder interlocked with a speed change control valve switched by a main speed change lever, and a hydraulic clutch oil passage cutoff auxiliary change-over valve interlocked with the shuttle speed change lever and auxiliary speed change lever. CONSTITUTION:In the non-operated state of an auxiliary speed change lever and a shuttle speed change lever, microswitches 35, 36 are switched on, so that an auxiliary change-over valve 30a communicates an oil passage 34 with an oil pump 29. Oil pressure set by a pressure control valve 30b is thereby supplied to a speed change control valve 31, a main change-over valve 32 and a pilot pressure control valve 33. The oil passage 34 is drained, and the oil passage 45 of the main change-over valve 32 is cut off to place a hydraulic clutch 11 in the cut-off state. On the other hand, the microswitches 35, 36 are switched off by the changeover operation of the shuttle speed change lever and auxiliary speed change lever so as to stop current application to the auxiliary change-over valve 30a. The oil passage 34 is thereby communicated with the drain side, and the main change-over valve 32 is switched in such a way as to cut off the hydraulic clutch 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission which is installed in a traveling drive system of a tractor together with a hydraulic clutch, and more specifically, to operate various levers for gear shifting so as to achieve clutchless operation during gear shifting. The present invention relates to a transmission of a tractor, which is configured to engage and disengage a hydraulic clutch in conjunction with.

[0002]

2. Description of the Related Art Generally, a tractor is provided with a traveling drive system for rotationally driving wheels, and a PTO drive system for rotationally driving a PTO shaft which is a power source of a working machine or the like, and these are connected via a main clutch. Configured to connect to the engine. The traveling drive system is provided with a transmission having a main transmission mechanism, an auxiliary transmission mechanism, a forward / reverse switching mechanism, and the like together with a hydraulic clutch, and a gear shift operation can be performed by disengaging the hydraulic clutch.

Heretofore, it has been conventionally proposed that the hydraulic clutch is connected to and disengaged from a shift lever of a transmission to achieve a so-called no-clutch operation during a shift operation. In addition, Japanese Utility Model Publication No. 62-25930 discloses that
When a transmission unit for ultra-deceleration, which is rarely used, is provided in the transmission, the transmission unit for ultra-deceleration is configured to be mechanically operated, and the hydraulic clutch is automatically disengaged by a switching valve linked to the operation. It is shown that the structure is simplified and the cost is reduced.

[0004]

By the way, in the technique described in the above publication, only the super-deceleration speed change portion provided in the transmission is mechanically operated, and the operating actuator (hydraulic actuator) is unnecessary. Regarding the forward / reverse switching operation, the structure is such that the forward / reverse switching actuator is driven via the forward / rearward switching valve. Therefore, it is difficult to say that the number of actuators used is large and the device configuration is sufficiently compact.

Further, since the forward / reverse switching operation is constituted by the hydraulic operation like the main shift operation and the sub shift operation,
Due to the arrangement of the valves and actuators used for this, the degree of freedom in the arrangement cannot be expected for the lever for forward / reverse switching operation.

In view of the above, the present invention provides a tractor which can achieve a so-called clutchless operation at the time of gear shift operation, has a compact device configuration, and has a degree of freedom in arranging the shuttle gear shift lever and the sub gear shift lever with respect to the main gear shift lever. An object is to provide a transmission.

[0007]

To this end, the present invention relates to a transmission which is provided in a traveling drive system of a tractor together with a hydraulic clutch, the first and second main transmission mechanisms and the first sub transmission. A main gearshift lever corresponding to the gearshift mechanism, a shuttle gearshift lever for switching the forward / reverse switching mechanism via a shift rail, and a sub gearshift lever for gearshifting the second auxiliary gearshift mechanism via the shift rail are provided. In the transmission,
A shift control valve which is switched by the main shift lever, a main shift valve which interlocks with the shift control valve and switches the oil passage of the hydraulic clutch from a connected state to a cutoff state at least during the shift operation, and the shift control Each hydraulic actuator that operates to shift the first and second main transmission mechanisms and the first auxiliary transmission mechanism in accordance with the switching position of the valve and the shift rail of the shuttle transmission lever or the auxiliary transmission lever are interlocked. The means is to provide a hydraulic control device having a sub switching valve for switching the oil passage of the hydraulic clutch from the connected state to the disconnected state during the switching operation.

More specifically, in the main switching valve of the hydraulic control device, the drain pressure of the drain line and the spring pressure are opposed to the pilot pressure of the pilot line, and when the pilot pressure is released, the hydraulic pressure is restored. In the switching state by the pilot pressure in which the oil passage of the clutch is shut off and the drain pressure is eliminated, a pilot switching valve that connects the oil passage of the hydraulic clutch is used, and the pilot pressure of this pilot switching valve is at least linked with the shift control valve. A pilot pressure control valve that depressurizes during the switching operation and each drain pressure control valve that depressurizes the drain pressure of the pilot switching valve only when the operation of the hydraulic actuator is completed are provided. As a means.

[0009]

With such means, the shift control valve is switched when the main shift lever is operated. Then, during the switching operation of the shift control valve, the main switching valve switches the oil passage of the hydraulic clutch to the disengaged state so that the hydraulic clutch is disengaged. Therefore, the first and second main speed change mechanisms and the first sub speed change mechanism are operated to change gears by hydraulic actuators that operate according to the switching position of the speed change control valve.

When the shuttle shift lever or the sub shift lever is operated, the corresponding shift rails are switched. And during this shift rail switching operation,
The sub switching valve switches the oil passage of the hydraulic clutch to the disengaged state to disengage the hydraulic clutch. Therefore, the forward / reverse switching mechanism is switched via the shift rail by the operation of the shuttle shift lever, and the second auxiliary transmission mechanism is shifted through the shift rail by the operation of the auxiliary shift lever.

As described above, the gear shifting operation of the first and second main transmission mechanisms and the first sub-transmission mechanism, which require continuous gear shifting and are frequently used, is performed by operating one main gear shifting lever. The hydraulic clutch is automatically disengaged, and the switching operation of the forward / reverse switching mechanism and the shift operation of the second auxiliary transmission mechanism are performed automatically by operating the shuttle shift lever or the auxiliary shift lever, respectively. Since it is performed in the state of being cut off, the so-called clutchless operation at the time of gear shift operation is achieved.

Here, the hydraulic actuator is used only for the speed change operation of the first and second main speed change mechanisms and the first auxiliary speed change mechanism, which are frequently used, and the switching operation of the forward and reverse switching mechanism and the second auxiliary speed change mechanism. Since the structure is not used for the speed change operation of the speed change mechanism, the device structure is compact and inexpensive.

Further, since the shuttle shift lever and the auxiliary shift lever are each manually operated via the shift rails, the shuttle shift lever and the auxiliary shift lever can be arranged separately from the hydraulically-operated main shift lever, and a degree of freedom in arrangement is obtained. To be

If the main switching valve is a pilot switching valve having a construction in which the drain pressure of the drain line and the spring pressure oppose the pilot pressure of the pilot line, the drain pressure opposing the pilot pressure should be low. Therefore, it is possible to reduce the leak of each drain pressure control valve that holds this drain pressure and sufficiently secure the drain pressure control performance.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 2 shows a schematic structure of a tractor to which one embodiment is applied. In this tractor 1, a main gear shift lever 3, a sub gear shift lever 4, and a shuttle gear shift lever 5 are separately arranged on a side of a driver seat 2. To prepare.

The drive system of the tractor 1 will be briefly described with reference to FIG.
The transmission 8 connected via the second main transmission mechanism 9, the first main transmission mechanism 10, the hydraulic clutch 11, the forward / reverse switching mechanism 12, the first auxiliary transmission mechanism 13, the second auxiliary transmission mechanism 14, Rear wheel 1 of tractor 1 via differential device 15
By being configured for transmission, the traveling drive system for rotationally driving the drive wheels is configured. Further, the transmission 8 is the first
By being configured to be transmitted to the PTO shaft 21 through the PTO speed change mechanism 17, the second PTO speed change mechanism 18, the transmission shaft 19, and the third PTO speed change mechanism 20, the PTO that serves as a power source for the working machine or the like.
A PTO shaft drive system that rotationally drives the shaft 21 is configured.

The first main transmission mechanism 10 switches from the neutral speed to the first speed or the second speed.
A gear shift operation is performed by a first hydraulic cylinder 22 as a hydraulic actuator. The second main transmission mechanism 9 switches from the neutral speed to the third speed or the fourth speed, and serves as a second hydraulic actuator.
A gear shift operation is performed by the hydraulic cylinder 23. Further, the first auxiliary transmission mechanism 13 switches the output rotation of the forward / reverse switching mechanism 12 between the high and low stages of H stage and L stage, and the third hydraulic cylinder 2 as a hydraulic actuator.
The gear shift operation is performed by means of 4. The operation of the first hydraulic cylinder 22, the second hydraulic cylinder 23, and the third hydraulic cylinder 24 is adapted to be controlled according to the switching position of a shift control valve, which will be described later, which is switched by the main shift lever 3. There is.

The forward / reverse switching mechanism 12 transfers the output rotation of the hydraulic clutch 11 as it is or reverses it and transmits it to the first sub transmission mechanism 13, and via a shift rail 25 interlocking with the shuttle transmission lever 5. It is designed to be switched. Further, the second auxiliary transmission system 14 switches the output rotation of the first auxiliary transmission system 13 between the high and low stages of H stage and L stage, and shifts via the shift rail 26 interlocked with the auxiliary transmission lever 4. It is designed to be operated.

FIG. 1 shows an on / off control of the hydraulic clutch 11.
And the first to third hydraulic cylinders 22 to 24
2 shows a hydraulic circuit of a hydraulic control device that controls the operation of the. This hydraulic circuit is shared with the hydraulic control devices 27 and 28 of the power steering device and the quick turn device equipped in the tractor 1, and the hydraulic oil from the oil pump 29 is also supplied to these hydraulic control devices 27 and 28. It is provided with a flow dividing valve 30 to be supplied, and a shift control valve 31, a main switching valve 32 and a pilot pressure control valve 33 to which pressure oil is directly supplied via the flow dividing valve 30. The hydraulic clutch 11 is connected via the main switching valve 32, and the first hydraulic cylinder 22 and the second hydraulic cylinder 23 are connected via the shift control valve 31.
The third hydraulic cylinders 24 are connected to each other.

The diversion valve 30 is connected to an oil pressure control device 28, a shift control valve 31, a main switching valve 32, and an oil passage 34.
An auxiliary switching valve 30a is provided downstream of the pressure control valve 30b to connect the oil pump 29 to the oil pump 29 side or the drain side for communication. The sub switching valve 30a is a spring return type electromagnetic switching type, which communicates the oil passage 34 to the drain side in the spring return state, and connects the oil passage 34 to the oil pump 29 when energized.
It is designed to communicate to the side. Micro switches 35 and 36 for controlling the energization of the sub switching valve 30a are provided in contact with the shift rails 25 and 26 to detect the movement of the shift rails 25 and 26, respectively, and the switching operation of the shuttle shift lever 5 and the sub shift lever 4 are performed. During the gear shift operation, the micro switch 35 or the micro switch 36 having a normally closed contact is turned off and the sub switching valve 30a is spring-restored to connect the oil passage 34 to the drain side.

The shift control valve 31 is of a rotary switching type in which N (neutral) and F1 to F8 switching positions are continuous, and is switched by the main shift lever 3. The expansion / contraction of the first hydraulic cylinder 22, the second hydraulic cylinder 23, and the third hydraulic cylinder 24 is controlled according to each switching position of the shift control valve 31. For example, in the N position, the first hydraulic cylinder 22 and the second hydraulic cylinder 22
By controlling both the hydraulic cylinders 23 to the intermediate extended position, both the first main transmission mechanism 10 and the second main transmission mechanism 9 are operated to shift to the neutral stage. Also, N, F1, F
In each of the switching positions of 2, F3, F4, the third hydraulic cylinder 24
Is extended and the first auxiliary transmission system 13 becomes a low speed L stage, and F
At each of the switching positions of 5, F6, F7, and F8, the third hydraulic cylinder 24 contracts, and the first auxiliary transmission mechanism 13 becomes the high speed H stage. Then, at the switching position of F1, F2, F5, F6, the second
While the main transmission mechanism 9 is in the neutral gear, the first hydraulic cylinder 22 is controlled to expand and contract, and the first main transmission mechanism 10 is in the first and second gear positions at the switching positions of F1 and F5, and in the switching positions of F2 and F6. The gears are respectively shifted to the second speed. Also, F
At the switching positions of 3, F4, F7 and F8, the first main transmission mechanism 1
0 is the neutral stage, while the second hydraulic cylinder 23 is controlled to expand and contract so that the second main transmission mechanism 9 operates at F3.
At the switching position of F7, the speed is changed to the third speed, and at the switching positions of F4 and F8, the speed is changed to the fourth speed.

The shift control valve 31 is provided with a cam 31a which moves according to each switching position, and the pilot pressure control valve 33 is in contact with the cam 31a. The pilot pressure control valve 33 is a spring return type two-position switching valve that controls the drainage of pressure oil in the oil passage 34 and its stop. When the speed change control valve 31 is in each of the N and F1 to F8 switching positions. The cam 31a performs a switching operation against the spring pressure to drain the pressure oil in the oil passage 34, and when the shift control valve 31 is switched, the spring is restored to stop the draining of the oil passage 34. It has become.

The main switching valve 32 is connected to the drain line 3 against the pilot pressure of the pilot line 37 communicating with the oil passage 34.
8 is a spring-return type two-position pilot switching valve in which the drain pressure and the spring pressure oppose each other, and the oil passage 34 and the oil passage 45 on the hydraulic clutch 11 side are communicated with each other via the main switching valve 32. . The main switching valve 32 disconnects the oil passage 34 and the oil passage 45 to disconnect the hydraulic clutch 11 in the spring return state where the pilot pressure in the pilot line 37 is depressurized, and the drain pressure in the drain line 38 disappears. When the pressure is switched by the pilot pressure of the pilot line 37, the oil passage 34 and the oil passage 45 are communicated with each other to bring the hydraulic clutch 11 into the connected state.

Here, the drain line 38 of the main switching valve 32
Communicates with an oil pan or the like through a check valve 39 which is closed by the weight of the ball and opened by a low suction force, and when the main switching valve 32 returns to the spring, oil is sucked up to the drain line 38 to secure the drain pressure. It is like this. Further, drain pressure control valves 41, 42, 43 are provided in a drain passage 40 branched from the drain line 38. These drain pressure control valves 41, 42, 43 are spring return type two-position switching valves that switch between disconnection and communication of the drain passage 40.
The drain passage 40 is blocked by a spring-biased ball closing the passage. The drain pressure control valve 41 is installed such that the piston rod of the second hydraulic cylinder 23 can be switched so that the drain pressure control valve 41 is spring-returned only at the extension limit and contraction limit of the second hydraulic cylinder 23 to communicate with the drain passage 40. Has been done. The drain pressure control valves 42 and 43 are also installed in the same manner so that the first hydraulic cylinder 22 and the third hydraulic cylinder 24 are spring-returned only at the extension limit and contraction limit of the first hydraulic cylinder 22 and the third hydraulic cylinder 24, respectively, to communicate the drain passage 40. .

A boost control valve 44 is connected to the main switching valve 32. The pressure-increasing control valve 44 controls the drain so that the pressure of the pressure oil supplied to the hydraulic clutch 11 gradually increases. The pressure oil in the oil passage 34 is drained at a pressure lower than the pressure set by the pressure control valve 30b. A spring-returning internal pilot type pressure control valve 44a, an accumulator 44b that supplies a pressure that opposes the pilot pressure of the pressure control valve 44a, and the accumulator 4
Orifice switching valve 44 for supplying pressure of oil passage 34 to 4b
and c. The orifice switching valve 44c is a spring return type pilot switching valve, and the pilot line 44d thereof has the shift control valve 31 and the third hydraulic cylinder 24.
It is connected to the oil passage that connects with. The orifice switching valve 44c supplies pressure oil to the accumulator 44b via the small-diameter orifice in the spring returning state, and the third
When the hydraulic cylinder 24 contracts and the first sub transmission mechanism 13 is shifted to the H stage, the operating pressure supplied to the third hydraulic cylinder 24 is used as a pilot pressure to perform a switching operation, and a large diameter orifice is used. Pressure oil is supplied to the accumulator 44b.

Next, the operation of the transmission 8 of the tractor of the embodiment thus constructed will be described. First, the micro switches 35 and 36 are turned on when the sub shift lever 4 or the shuttle shift lever 5 is not operated, and the sub switching valve 30a causes the oil passage 34 to flow through the oil pump 2.
It has been switched to communicate with the 9 side. Therefore, the pressure control valve 31, the main switching valve 32, and the pilot pressure control valve 33 are directly supplied with the pressure oil having the pressure set by the pressure control valve 30b. In such a state, when the main shift lever 3 is in the N position, that is, the shift control valve 31 is switched to the N position, the first hydraulic cylinder 22 and the second hydraulic cylinder 23.
Are controlled to the intermediate extended position, so that the first main transmission mechanism 10 and the second main transmission mechanism 9 are both in the neutral stage. At this time, the pilot pressure control valve 33
Drains the pressure oil in the oil passage 34, so that the pilot pressure in the pilot line 37 is extinguished. Therefore, the main switching valve 32
Disconnects the oil passage 45, and the hydraulic clutch 11 is in the disconnected state.

Next, when the shift control valve 31 is switched to the F1 position by the main shift lever 3, the pilot pressure control valve 33
Stops the drain of oil passage 34, so pilot line 3
The pressure oil in the oil passage 34 is supplied to the valve 7 to generate the pilot pressure.
Is still below the contraction limit, the drain pressure control valve 42
Keeps the drain line 38 closed. Therefore, the main switching valve 32 still keeps the oil passage 45 blocked,
The hydraulic clutch 11 is in the disengaged state. Therefore, the first hydraulic cylinder 22 contracts according to the F1 position of the shift control valve 31, and the first main transmission mechanism 10 shifts to the first speed, and the third main shift mechanism 10 shifts to the third speed.
The hydraulic cylinder 24 extends and the first auxiliary transmission mechanism 13 is operated to shift to the low L stage. Upon completion of this shift operation, the drain pressure control valves 42 and 43 open the drain line 38, the drain pressure is extinguished, the main switching valve 32 is switched by the pilot pressure, and the oil passage 34 and the oil passage 45 communicate with each other. Then, the hydraulic clutch 11 is connected.

When connecting the hydraulic clutch 11 as described above, the orifice switching valve 44c of the boost control valve 44 is switched so as to select a small-diameter orifice by the pilot pressure supplied by the pilot line 44d. The pressure of the pressure oil supplied to 11 gradually increases at a relatively slow rate over a relatively long period of time. Therefore, the hydraulic clutch 11 is connected in a state with less shock and transmits the power of the engine 6 to the rear wheels 16 without stall.

Further, even when the shift control valve 31 is switched to the F2 position or the F8 position by the main shift lever 3, the main shift valve 32 performs the switching operation in the same manner as described above and the hydraulic clutch 11 is automatically disengaged. To do. In this case, the shift control valve 3
When the pilot pressure control valve 33 drains the pressure oil in the oil passage 34 in synchronism with the switching operation of No. 1 and the pilot pressure of the pilot line 37 is extinguished, the main switching valve 32 returns to the spring and opens at a low pressure. Drain line 38 through 39
Inhale. Therefore, after the pilot pressure control valve 33 stops the drain of the oil passage 34, the main switching valve 32 secures the drain pressure until the drain pressure control valves 41 and 42 open the drain line 38 to ensure the oil passage 45. Can be shut off. Further, since the check valve 39 dedicated for securing such a drain pressure is provided, the drain pressure control valve 4
1, 42, 43 can make the drain passage 40 blocking structure a check valve structure by a spring-biased ball, and can surely prevent leakage by setting the drain line 38 to a low pressure.

Here, when the shift control valve 31 is switched to the F5 position to the F8 position, that is, the first auxiliary transmission mechanism 1
When the speed of the tractor 1 in the state in which 3 is shifted to the high speed H stage is relatively high, the third hydraulic cylinder 24 is controlled to contract by the supply of hydraulic oil, and the hydraulic oil pressure thereof becomes the pilot pressure. It acts on the orifice switching valve 44c.
Therefore, the orifice switching valve 44c switches to select a large-diameter orifice, and the pressure of the pressure oil supplied to the hydraulic clutch 11 via the main switching valve 32 gradually increases at a slightly higher speed. . Therefore, the hydraulic clutch 11
Quickly and automatically connects the power of the engine 6 to the rear wheels 1
6 will be transmitted.

On the other hand, when the shuttle transmission lever 5 is switched, the shift rail 25 moves to turn off the micro switch 35 and de-energize the sub switching valve 30a. Therefore, the sub switching valve 30a returns to the spring to communicate the oil passage 34 to the drain side, and the pilot pressure in the pilot line 37 is extinguished, so that the main switching valve 32 switches to disconnect the hydraulic clutch 11. . So hydraulic clutch 1
1 is quickly shut off, and the forward / reverse switching mechanism 12 is switched by the shift rail 25 to either the forward speed or the reverse speed.
When this switching operation is completed, the micro switch 3
5 is turned on, the sub switching valve 30a is energized, and the oil passage 34 is switched to the oil pump 29 side via the pressure control valve 30b.
Then, the pilot pressure is generated in the pilot line 37, and the main switching valve 32 is switched to connect the hydraulic clutch 11, and thus the hydraulic clutch 11 is switched to the orifice switching valve 4.
4c is connected at a predetermined speed according to the switching position.

When the sub gear shift lever 4 is switched,
When the shift rail 26 moves, the micro switch 3
6 is turned off and the auxiliary switching valve 30a is de-energized. Therefore, similarly to the operation of the shuttle gear shift lever 5, the hydraulic clutch 11 is immediately disengaged, and the shift rail 26 switches the second auxiliary transmission mechanism 14 to the high speed H stage or the low speed L stage. When this switching operation is completed, the micro switch 36 is turned on and the sub switching valve 30a is energized, so that the main switching valve 32 is switched to connect the hydraulic clutch 11, and thus the hydraulic clutch 11 becomes the orifice switching valve 44c. Connection is made at a predetermined speed according to the switching position.

As described above, in this embodiment, the first main transmission mechanism 10, the second main transmission mechanism 9 and the first sub transmission mechanism 13 are required to be continuously operated and frequently used.
The gear shift operation is performed by automatically controlling the hydraulic clutch 11 to be intermittently operated by operating one main gearshift lever 3. Also,
Switching operation of the forward / reverse switching mechanism 12 and the second auxiliary transmission system 14
The gear shift operation is performed by automatically controlling the hydraulic clutch 11 to be intermittently operated by operating the shuttle gear shift lever 5 or the auxiliary gear shift lever 4, respectively, so that a so-called no clutch operation is achieved.

Here, the first hydraulic cylinders 22, 23, 2
4 is used only for shifting operations of the first main transmission mechanism 10, the second main transmission mechanism 9 and the first auxiliary transmission mechanism 13 which are frequently used, and the switching operation of the forward / reverse switching mechanism 12 and the second auxiliary transmission. Since the structure is not used for the gear shifting operation of the lecture 14, the device structure is inexpensive and compact.

Further, since the shuttle transmission lever 5 and the auxiliary transmission lever 4 are manually operated by operating via the shift rails 25 and 26, respectively, they can be arranged and arranged separately from the hydraulically operated main transmission lever 3. Gives you more freedom.

[0036]

As described above, according to the present invention, when the main transmission lever is operated, the transmission control valve is switched, and during the switching operation, the main switching valve switches the oil passage of the hydraulic clutch to the disconnected state. The hydraulic clutch is disengaged. Therefore, the first and second main speed change mechanisms and the first sub speed change mechanism are operated to change gears by hydraulic actuators that operate according to the switching position of the speed change control valve.

When the shuttle gear shift lever or the sub gear shift lever is operated, the corresponding shift rails perform a switching operation. During this switching operation, the sub switching valve switches the oil passage of the hydraulic clutch to the disengaged state so that the hydraulic clutch operates. Be cut off. Therefore, the forward / reverse switching mechanism is switched via the shift rail by the operation of the shuttle gearshift lever.
The second subtransmission mechanism is operated to shift gears by operating the subtransmission lever.

In this way, continuous gear shifting is required, and the gear shifting operations of the first and second main gear shifting mechanisms and the first sub gear shifting mechanism which are frequently used are performed by operating one main gear shifting lever. The hydraulic clutch is automatically disengaged, and the switching operation of the forward / reverse switching mechanism and the shift operation of the second auxiliary transmission mechanism are performed automatically by operating the shuttle shift lever or the auxiliary shift lever, respectively. Since the operation is performed in the closed state, the so-called clutchless operation can be achieved.

Here, the hydraulic actuator is used only for the speed change operation of the first and second main speed change mechanisms and the first sub speed change mechanism, which are frequently used, and the switching operation of the forward / reverse speed change mechanism and the second auxiliary speed change mechanism. Since the structure is not used for the speed change operation of the speed change mechanism, the device structure can be made inexpensive and compact.

Further, since the shuttle shift lever and the auxiliary shift lever are each manually operated via the shift rails, they can be arranged separately from the hydraulically operated main shift lever, and a degree of freedom in arrangement is obtained. To be

When the main switching valve is a pilot switching valve having a construction in which the drain pressure of the drain line and the spring pressure oppose the pilot pressure of the pilot line, the drain pressure opposing the pilot pressure should be low. Therefore, it is possible to reduce the leak of each drain pressure control valve that holds this drain pressure and sufficiently secure the drain pressure control performance.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a hydraulic control device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a tractor to which an embodiment is applied.

FIG. 3 is a schematic configuration diagram of a drive system of a tractor to which an embodiment is applied.

[Explanation of symbols]

1 tractor 3 Main shift lever 4 Sub shift lever 5 Shuttle shift lever 8 gearbox 9 Second main speed change mechanism 10 First main transmission mechanism 11 hydraulic clutch 12 Forward / reverse switching mechanism 13 1st auxiliary transmission lecture 14 Second auxiliary transmission course 22 1st hydraulic cylinder 23 Second hydraulic cylinder 24 Third hydraulic cylinder 25 shift rails 26 shift rails 30 shunt valve, 30a Sub switching valve 31 Shift control valve 32 Main switching valve 33 Pilot pressure control valve 34 oil passage 37 Pilot line 38 Drain line 45 oil passage

Claims (2)

[Claims] 1. A transmission, which is interposed in a traveling drive system of a tractor together with a hydraulic clutch, wherein main transmission levers corresponding to first and second main transmission mechanisms and a first sub transmission mechanism are provided.
In a transmission equipped with a shuttle shift lever for switching a forward / reverse switching mechanism via a shift rail and an auxiliary shift lever for shifting a second auxiliary shift mechanism via a shift rail, switching is performed by the main shift lever. Depending on the operated shift control valve, the main switching valve that interlocks with the shift control valve and switches the oil passage of the hydraulic clutch from the connected state to the disconnected state at least during the switching operation, and the switching position of the shift control valve. The hydraulic actuators that operate to shift the first and second main transmission mechanisms and the first sub transmission mechanism, respectively, and the switching operation in conjunction with the shift rails of the shuttle shift lever or the sub shift lever. Is provided with a hydraulic control device having an auxiliary switching valve for switching the oil passage of the hydraulic clutch from the connected state to the disconnected state. Location. 2. The main switching valve of the hydraulic control device, wherein the drain pressure of the drain line and the spring pressure oppose the pilot pressure of the pilot line, and the oil pressure of the hydraulic clutch is restored when the pilot pressure is released and the spring is returned. In the switching state by the pilot pressure with the drain pressure extinguished, the pilot switching valve that connects the oil passage of the hydraulic clutch is used, and the pilot pressure of this pilot switching valve is linked to the shift control valve at least during the switching operation. Is provided with a pilot pressure control valve for extinguishing the pressure and each drain pressure control valve for extinguishing the drain pressure of the pilot switching valve only when the operation of the hydraulic switching actuator is completed. Item 1. A tractor transmission according to Item 1.