JP2003028294A - Circuit pressure enclosing prevention mechanism of hydraulic continuously variable transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that the input torque of a hydraulic continuously variable transmission is excessively increased at the time of restart of an engine and the engine cannot be started since the hydraulic pressure of a hydraulic servo mechanism is eliminated and a movable swash plate is disabled to rotatively return to a neutral position when a working vehicle having the hydraulic continuously variable transmission with the hydraulic servo mechanism for operating the movable swash plate is engine-stopped during running on a sloped or a flat road. SOLUTION: In HST10 for operating the swash plate angle of the movable swash plate 21c through the hydraulic servo mechanism 69, switching valves 11 are installed in the forward movement side and backward movement side circuits in main circuits 32R and 32L of the HST10 so that the forward and backward movement circuits can be communicated with a drain circuit 32d. The switching valves 11 are installed on an oil passage plate 31 having a main circuit formed therein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for preventing circuit pressure closing of a main circuit in a hydraulic continuously variable transmission.

[0002]

2. Description of the Related Art Conventionally, in a hydraulic continuously variable transmission which is composed of a hydraulic pump and a hydraulic motor, for example, the hydraulic pump is a variable displacement pump, the swash plate angle of the movable swash plate of the hydraulic pump is There has been one in which control is performed via a hydraulic servo mechanism provided in a hydraulic continuously variable transmission. When a work vehicle equipped with a hydraulic continuously variable transmission that tilts the movable swash plate via this hydraulic servo mechanism stops the engine while running on a slope or a flat road, the hydraulic servo mechanism loses its hydraulic pressure. , Even if the operation lever of the movable swash plate is returned to the neutral position, the movable swash plate cannot be rotated to return to the neutral position, and the hydraulic pressure is trapped in the main circuit of the hydraulic continuously variable transmission. The input and output shafts were locked. As described above, when the engine is started in the locked state, the input torque of the hydraulic continuously variable transmission becomes excessive and the engine cannot be started.

[0003]

As described above, in order to release the locked state due to the closing of the hydraulic pressure when the engine is stopped, a valve is conventionally provided in the main circuit of the hydraulic continuously variable transmission, 2. Description of the Related Art A hydraulic continuously variable transmission has been devised, which is configured to open a closing pressure of a main circuit by opening and closing a valve. However, since the valve for releasing the closing pressure connects the forward side main circuit and the reverse side main circuit to each other and simultaneously connects the drain circuit, the forward side circuit or the reverse side circuit is connected. Either one could not be selectively opened.
Further, the valve for releasing the closing pressure is to be attached externally to the hydraulic continuously variable transmission and requires external piping, so that high pressure applied to the piping causes damage such as cracks, There was a problem that oil might leak from the connection part of the pipe.

[0004]

The problems to be solved by the present invention are as described above. Next, the means for solving the problems will be described. That is, in claim 1, in the hydraulic continuously variable transmission that operates the swash plate angle via the hydraulic servo mechanism, the forward side circuit and the reverse side circuit in the main circuit of the hydraulic continuously variable transmission are respectively provided. A switching valve is provided so that the forward side circuit, the reverse side circuit and the drain circuit can communicate with each other, and the forward side circuit switching valve and the reverse side circuit switching valve are respectively configured as separate switching valves. The valve was mounted on the oil path plate where the main circuit was formed.

According to a second aspect of the present invention, in a hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, a forward circuit or a reverse circuit in a main circuit of the hydraulic continuously variable transmission. One check / relief valve is provided with a throttle part that connects the main circuit and the charge circuit, and a switching valve is provided on the other of the forward circuit and the reverse circuit to enable communication with the drain circuit. It was attached to the oil passage plate where the main circuit is formed.

According to another aspect of the present invention, the switching valve is linked with an engine starter connected to the hydraulic continuously variable transmission so that the main circuit and the drain circuit communicate with each other when the starter operates. Configured to.

According to a fourth aspect of the present invention, in a hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, a forward circuit or a backward circuit in a main circuit of the hydraulic continuously variable transmission. An oil for forming a main circuit by providing a switching valve on one side so that one of the forward side circuit and the reverse side circuit can communicate with the drain circuit, and the switching valve is configured as a 2-position 4-port electromagnetic switching valve. It was mounted on a road plate, and the P port and one of the A port and the B port of the switching valve were connected to one of the forward side circuit and the reverse side circuit, and the other of the A port and the B port was connected to the drain circuit.

Further, according to the present invention, a throttle portion is provided in the middle of the drain circuit.

Further, in the present invention, the switching valve is a manual switching valve.

According to a seventh aspect of the present invention, in a hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, an opening / closing valve that uses a charge pressure as a pilot pressure is provided, and the opening / closing valve is used when the charge pressure decreases. The valve is opened so that the forward side circuit and the reverse side circuit in the main circuit communicate with each other, and when the charge pressure rises, the opening / closing valve is closed so that the forward side circuit and the reverse side circuit in the main circuit are separated from each other.

Further, according to the present invention, in a hydraulic type continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, an on-off valve that uses a charge pressure as a pilot pressure is provided, and when the charge pressure drops, The charge relief valve provided between the main circuit and the charge circuit is opened by the opening / closing valve so that the main circuit and the charge circuit are communicated with each other.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described. FIG. 1 is a circuit diagram showing a hydraulic continuously variable transmission equipped with a circuit pressure closing prevention mechanism of the present invention, FIG. 2 is a front sectional view showing an oil passage plate of the hydraulic continuously variable transmission, and FIG. 3 is a check relief. FIG. 4 is a side sectional view showing a valve, FIG. 4 is a side sectional view showing a two-position two-port type switching valve, and FIG. 5 is a second embodiment of a hydraulic continuously variable transmission equipped with a circuit pressure closing prevention mechanism. 6 is a front sectional view showing an oil passage plate of the hydraulic continuously variable transmission in FIG. 5, and FIG. 7 is a third embodiment of the hydraulic continuously variable transmission having a circuit pressure closing prevention mechanism. FIG. 8 is a front sectional view showing an oil passage plate of the hydraulic continuously variable transmission in FIG. 7, FIG. 9 is a side sectional view showing a 2-position 4-port type switching valve, and FIG. An oil passage plate in a hydraulic continuously variable transmission according to a fourth embodiment having a circuit pressure closing prevention mechanism is shown. Front sectional view, FIG. 11 is a front sectional view showing an oil path plate in the hydraulic stepless transmission of the fifth embodiment with a preventing mechanism narrowing Ji circuit pressure closed.

A hydraulic continuously variable transmission having a circuit pressure closing prevention mechanism of the present invention will be described. 1 and 2
As shown in FIG. 1, the hydraulic continuously variable transmission (hereinafter referred to as HST) 10 is composed of a variable displacement hydraulic pump 21 and a hydraulic motor 22, and the swash plate angle of the movable swash plate 21 c of the variable displacement hydraulic pump 21 is Are configured to be controlled via the hydraulic servo mechanism 69.

The hydraulic pump 21 and the hydraulic motor 22 are connected by main circuits 32R and 32L.
One of the main circuits 32R and 32L is a forward circuit,
The other is the reverse circuit. The main circuit 32R / 3
Check / relief valves 35, 35 are interposed between 2L and the charge circuit 32c to which the charge pressure by the charge pump 51 is applied.

When the hydraulic oil in the main circuits 32R and 32L is insufficient, the check relief valve 35 supplies the hydraulic oil from the charge circuit 32c to the main circuits 32R and 32L via the check / relief valve 35. Is configured. In addition, the main circuit 32R / 32
The check / relief valve 35 is opened to release the hydraulic oil to the charge circuit 32c when the pressure L becomes larger than a certain value. That is, the check / relief valve 35 has both a check valve function and a relief valve function. The charge circuit 32c is provided with a relief valve 36 in the circuit leading to the check valves 35, 35.
The hydraulic pressure inside is adjusted.

The HST 10 is also provided with a hydraulic servo mechanism 69 for controlling the swash plate angle of the movable swash plate 21c of the hydraulic pump 21, and the hydraulic servo mechanism 69 is connected to the servo control passage from the charge pump 51. Servo control pressure is supplied through 75. In the hydraulic servo mechanism 69, the spool 72 is slidably operated by the turning operation of the operation lever 20 to supply the servo control pressure to the upper pressure chamber 70a or the lower pressure chamber 70b of the piston chamber 70, and the piston 71 is moved. The movable swash plate 21c is slid to control the swash plate angle.

As shown in FIG. 3, the check / relief valve 35 includes the main circuits 32R and 32 of the HST 10.
It is configured in the valve hole 32h of the oil passage plate 32 in which L is formed. A valve member 52 is slidably fitted in an inner end portion of the valve hole 32h, and a plug 56 is screwed in an outer end portion of the valve hole 32h, and a storage hole 56a formed in the plug 56. A spring receiving member 55 is slidably fitted therein. A check spring 57 is housed in a space inside the housing hole 56a closed by the spring receiving member 55, and the space is configured as a check spring chamber 61.

A relief spring 54 is interposed between the spring receiving member 55 and the valve member 52, and the spring receiving member 55 and the valve member 52 on which the relief spring 54 is disposed.
A space inside the valve hole 32h surrounded by and is configured as a relief spring chamber 62. The relief spring chamber 62 communicates with the main circuits 32R and 32L. In addition, a fitting gap is formed between the peripheral surface of the portion of the plug 56 where the storage hole 56a is formed and the spring receiving member 55, and the relief spring chamber 62 and the check spring chamber 61 are in communication with each other.

A relief pin 58 is fixed to the spring receiving member 55 so as to be slidable integrally therewith.
Reference numeral 8 extends through the communication hole 52a formed in the valve member 52 to connect the relief spring chamber 62 and the charge circuit 32c to the charge circuit 32c side. A head portion 58a is formed at the tip of the relief pin 58 (end on the check circuit 32c side). Since the relief pin 58 is biased toward the plug 56 side by the relief spring 54, the seat portion 58b of the head portion 58a is formed. The contact hole 52a of the valve member 52 is abutted against the peripheral edge portion of the communication hole 52a to close the communication hole 52a.

Then, the valve member 52 and the relief spring 5
4, the spring receiving member 55, and the relief pin 58 are integrally configured as a valve body 59 which is slidable in the valve hole 32h, and the valve body 59 is biased inward by the check spring 57. , The valve member 52 is the valve hole 3
It is in contact with the seat portion 53 at the inner end of 2h.

In the check / relief valve 35 constructed as described above, when the pressures in the main circuits 32R and 32L and the relief spring chamber 62 become high, the valve body 59 is pressed against the seat portion 53 and the charge circuit 32c is formed. The space between the relief spring chamber 62 and the relief spring chamber 62 is closed.

When the pressure in the main circuits 32R and 32L and in the relief spring chamber 62 becomes equal to or higher than the relief set pressure, the seat portion 5 of the head portion 58a of the relief pin 58.
The pressure applied to 8b becomes larger than the urging force of the relief spring 54, and the relief pin 58 causes the charge circuit 32 to move.
After moving to the c side, the communication hole 92a of the valve member 92 is opened, and the hydraulic oil in the main circuits 32R and 32L escapes to the charge circuit 32c side. That is, it acts as a relief valve.

Further, when the movable swash plate 21c of the hydraulic motor 21 is tilted, the main circuit 32R.
In 32L, the pressure drops due to a shortage of hydraulic oil in the main circuits 32R and 32L, and the charge circuit 32c
The valve body 59 is moved to the plug 56 side by the pressure of
The hydraulic oil is replenished from the charge circuit 32c to the main circuits 32R and 32L, and the pressure of the main circuits 32R and 32L and the pressure of the charge circuit 32c become the same pressure.

On the contrary, when the movable swash plate 21c of the hydraulic pump 21 is tilted and the valve body 59 is opened, the movable swash plate 21c is returned to the neutral state.
The low pressure state in R / 32L is released, and the check spring 5
The valve body 59 moves to the charge circuit 32c side by the urging force of 7, and the charge circuit 32c and the main circuits 32R and 32L are separated by the valve member 52 of the valve body 59.

A switching valve 11 is provided in each of the main circuits 32R and 32L. The switching valve 11 is configured as an electromagnetic valve that switches connection or disconnection between the main circuits 32R and 32L and the drain circuit 32d that communicates with the inside of the housing 31.

As shown in FIG. 4, the switching valve 11 is a two-position valve having a P port 11p connected to the main circuits 32R and 32L and an A port 11a connected to a drain circuit 32d communicating with the inside of the housing 31. It is configured as a 2-port type electromagnetic switching valve. Then, the spool 11d is slidingly controlled by the solenoid 11s, so that the P port 1
It is configured to switch connection or disconnection between 1p and the A port 11a, that is, connection or disconnection between the main circuits 32R and 32L and the drain circuit 32d.

Here, the HS equipped with the hydraulic servo mechanism 69
At T10, when the engine of the work vehicle in which the HST10 is mounted is stopped, the control pressure is not supplied to the hydraulic servo mechanism 69, so that the movable swash plate 21c cannot be operated. In this case, the hydraulic pressure in the main circuits 32R and 32L is
If the engine is restarted while the movable swash plate 21c is still tilted in the state of being confined in 32L, the input torque of the HST 10 becomes excessive and it becomes impossible to start the engine.

Therefore, in the HST 10, the solenoid 11s is turned off and the switching valve 11 is switched to the side where the main circuits 32R and 32L and the drain circuit 32d are separated while the engine is operating, and the engine is started. At times, the solenoid 11s is turned on and the main circuit 3
The switching valve 11 is configured to be switched to the side where the 2R / 32L and the drain circuit 32d are connected. By connecting the main circuits 32R / 32L and the drain circuit 32d, the hydraulic oil in the main circuits 32R / 32L flows into the housing 31 through the drain circuit 32d, and the closing pressure in the main circuits 32R / 32L is released. As a result, the input torque of the HST 10 is reduced and the engine can be started.

Since the switching valve 11 is provided in both the main circuit 32R and the main circuit 32L, it can be used both when the movable swash plate 21c is tilted forward and when it is tilted backward. In the case of, the main circuit 32R on the high voltage side
-The engine can be started by releasing the closing pressure of 32L. Also, the main circuit 3
Since the switching valve 11 provided in 2R and the switching valve 11 provided in the main circuit 32L are respectively configured as separate switching valves, only the main circuit on the necessary side of the main circuits 32R and 32L is opened. be able to.

The connection between the main circuits 32R and 32L and the drain circuit 32d when the engine is stopped may be made by an external pipe such as a bypass valve. There is a risk that oil will leak from damaged parts such as cracks that occur and the connection parts of pipes. However, in the HST 10, the switching circuit 11 connects the main circuits 32R and 32L and the drain circuit 32d when the engine is stopped, and the switching valve 11 is connected to the oil passage plate 32.
Since it is mounted on the external piping, there is no need for external piping, there is no concern about oil leakage, and noise can be reduced compared to the case of external piping.

Further, the switching valve 11 is interlocked with a starter motor for starting the engine of the working machine, and only when the starter motor is operating, the solenoid 11s is turned on to connect the main circuits 32R and 32L and the drain circuit 32d. Can be configured to be connected. Further, when the clutch which is a safety device at the time of starting the engine is depressed at the time of starting the engine, the solenoid 11s is turned on in association with the depression of the clutch, and the main circuit 32R.
32L and the drain circuit 32d may be connected to each other. With this configuration, the main circuit 32R / 32L and the drain circuit 3 are provided only when the engine is started.
Since the switching valve 11 is switched to the side to which 2d is connected, the main circuit 32R / 3 while the working machine is traveling.
It is possible to prevent an erroneous operation such as connecting the 2L and the drain circuit 32d, and it is possible to reduce fatigue of the switching valve 11 and improve durability.

Further, as shown in FIG. 1, the drain circuit 32
A throttle portion 32f is provided at d, and the switching valve 11 is switched to switch the main circuit 32R / 32L and the drain circuit 32d.
When the and are connected, the flow rate of the hydraulic oil in the main circuits 32R / 32L flowing into the housing 31 is limited, and a large amount of the hydraulic oil in the main circuits 32R / 32L is prevented from flowing into the housing 31. is doing.

As a result, for example, even if the engine is stopped while the working machine on which the HST10 is mounted is stopped on a slope, a large amount of hydraulic oil in the main circuits 32R and 32L will flow out and the braking action of the HST10 will occur. Disappears,
It is possible to prevent the work machine from starting to run and improve reliability.

Next, a second embodiment of the HST 10 will be described. In the HST 10 shown in FIGS. 5 and 6, one of the main circuits 32R and 32L (for example, the main circuit 32).
L) is provided with the switching valve 11, and the main circuit 32R / 3
The throttle hole 12 is provided in the other of the 2L (for example, the main circuit 32R). In this case, for example, the main circuit 32L provided with the switching valve 11 is a forward circuit and the main circuit 32R provided with the throttle hole 12 is a backward circuit.

The throttle hole 12 is a valve member 52 of the check / relief valve 35 provided on the main circuit 32R side.
When the communication hole 52a of the valve member 52 is closed by the head portion 58a of the relief pin 58, the main circuit 32R and the charge circuit 32c are communicated with each other by the throttle hole 12. Therefore, in the HST 10 shown in FIGS. 5 and 6, the trapping pressure in the main circuit 32R when the engine is stopped is gradually released to the charge circuit 32c through the throttle hole 12 and the main circuit 32L.
The internal closing pressure can be released by the switching valve 11 as described above.

As described above, by forming the throttle hole 12 in the check / relief valve 35 of the main circuit 32R or the main circuit 32L on the side where the switching valve 11 is not provided, the switching valve 11 provided in the HST 10 is unified. Therefore, the cost can be reduced. In addition, the check / relief valve 35 of the main circuit 32L on the reverse drive side may be provided with a throttle hole to secure the neutral position of the movable swash plate 21c. In this case, the throttle hole is closed. Since it can be used as the throttle hole 12 for releasing pressure, it is not necessary to form the throttle hole 12 specially, and further cost reduction can be achieved.

Next, a third embodiment of the HST 10 will be described. In the HST 10 shown in FIGS. 7 and 8, one of the main circuits 32R and 32L (for example, the main circuit 32).
L) is provided with the switching valve 13, and the main circuit 32R / 3
The throttle hole 1 is provided on the other side of 2L (for example, the main circuit 32R).
2 is provided. As shown in FIG. 9, the switching valve 13 has a P
It has a port 13p, a T port 13t, an A port 13a, and a B port 13b. The P port 13p and the B port 13b are connected to the main circuit 32L, and the A port 1
3a is connected to the drain circuit 32d.

Then, the main circuit 32L and the drain circuit 3
When the switching valve 13 is switched to the side where 2d is separated, the P port 13p and the B port 13b are communicated, the A port 13a and the T port 13t are communicated, and the T port 13t is The pressure in the housing 31 connected to the A port 13a through the drain circuit 32d is applied. In addition, the main circuit 32L and the drain circuit 3
When the switching valve 13 is switched to the side to which 2d is connected, the P port 13p and the A port 13a are in communication, and the B port 13b and the T port 13t are in communication. In this case, the main circuit 32L is the housing 31
It is connected to the inside and the closing pressure is released, and the T port 13t
Is connected to the main circuit 32L, the T port 13
The pressure in the housing 31 is applied to t.

Here, when pressure is applied to the T port 13t of the switching valve 13, the pressure is fitted into the solenoid 13s of the switching valve 13 and the respective ports 13a, 13b, 13p, 1 are attached.
It acts on the core tube portion 13k in which 3t is formed. Core tube part 13
Since the portion of the k that is fitted into the solenoid 13s does not have so much strength, the switching valve 13 may be damaged if a high pressure is applied to the T port 13t. Therefore, in the case where the main circuit 32L on the high-voltage side is applied to the T port 13t, the circuit pressure of the main circuit 32L cannot be set too high.

However, as described above, the switching valve 13 of this example is switched to the side where the main circuit 32L and the drain circuit 32d are separated, and the side where the main circuit 32L and the drain circuit 32d are connected. Since the pressure in the housing 31 on the low pressure side is applied to the T port 13t in both cases of switching to
The high voltage of the main circuit 32L is not applied to the T port 13t.

As described above, since the circuit pressure of the main circuit 32L is not applied to the T port 13t, it is possible to set the circuit pressure of the main circuit 32L without worrying about damage to the switching valve 13. It is possible to configure the HST 10 having a high voltage specification, in which is set to a high voltage.

Further, the switching valves 11 and 13 are
In this example, the solenoid valve is used, but a manual switching valve that switches connection / disconnection between the main circuit 32L and the drain circuit 32d by a manual operation may be used. In this case, for example, the switching valve and the engine starting operation unit are connected by a wire, a link, or the like, and the switching valve is operated on the side to which the main circuit 32L and the drain circuit 32d are connected only during the engine starting operation. To configure. In this way, the changeover valves 11 and 13 are manually operated, and the changeover valves 11 and 13 are operated by interlocking with the mechanical operation by an external force to operate the changeover valves 11 and 13. However, a power source such as a battery is unnecessary.

Next, a fourth embodiment of the HST 10 will be described. In the HST 10 shown in FIG. 10, an opening / closing valve 81 that uses the charging pressure as a pilot pressure is provided in the charging circuit 32c, and the closing pressure of the main circuits 32R and 32L is eliminated by the opening / closing valve 81.
This is because the main circuit 32R and the main circuit 32L are made to communicate with each other by the opening / closing valve 81, so that even when the input rotation is given in a state where the movable swash plate 21c is tilted, one of the main circuits 32R and 32L is in the compression process. Since the other main circuits 32L and 32R are in the expansion stroke, the closing is eliminated.

That is, the opening / closing valve 81 slidably accommodates the piston 81a in the charge circuit 32c. The valve portion 8 formed in a groove shape on the outer periphery of the upper and lower intermediate portions of the piston 81a.
1c, and the valve portion 81c is provided on the oil passage plate 32.
And communication paths 32s and 32s that allow communication with the main circuits 32R and 32L. The piston 81a is biased downward by a spring member 81b.
The open / close valve 81 is provided for the spring member 8 when the pressure in the charge circuit 32c is low, such as when the engine is stopped.
Due to the urging force of 1b, the valve portion 81c and each main circuit 32R
It is configured to slide downward to a position where 32L communicates with the communication passages 32s and 32s, that is, a position where the main circuit 32R communicates with the main circuit 32L. On the contrary, when the pressure in the charge circuit 32c is rising, such as during engine operation, the charge pressure causes the piston 8 to move.
1 slides upward against the biasing force of the spring member 81b. As a result, the valve portion 81c of the piston 81a and the communication passage 32s
The state where 32s is separated, that is, the main circuit 32R and the main circuit 32L are separated.

Thus, when the engine stops and the pressure in the charge circuit 32c decreases, the valve portion 81c of the on-off valve 81 allows the main circuit 32R and the main circuit 32L to communicate with each other. Even when the engine is stopped, the closing pressure of the main circuits 32R and 32L can be released, and the engine can be started easily.

Next, a fifth embodiment of the HST 10 will be described. In the HST 10 shown in FIG. 11, an opening / closing valve 91 that uses the charge pressure as a pilot pressure is provided in the charge circuit 32c so that the pressure in the main circuits 32R and 32L is not closed.

The on-off valve 91 accommodates the valve body 91 slidably in the charge circuit 32c. The valve body 91a is the head portion 58 of the relief pin 58 in the check / relief valve 35 of the main circuit 32R / 32L.
It is biased by the spring member 91b in the direction of abutting on a. The on-off valve 91 is configured such that when the pressure in the charge circuit 32c is reduced, such as when the engine is stopped, the valve body 91a is relieved by the urging force of the spring member 91b.
8 and the relief pin 58 is slid in the direction in which the valve member 52 opens, and the charge circuit 32c
And the main circuits 32R and 32L are communicated with each other. On the contrary, when the engine is operating, the charge circuit 3
When the pressure in 2c is increasing, the valve body 91 is slid in the direction opposite to the biasing direction of the spring member 91b by the charge pressure. As a result, the valve body 91 becomes the relief pin 5
8, the valve member 52 is closed away from the head portion 58a of 8, and the check / relief valve 35 performs a normal check function. In a normal state, the charge circuit 32c and the main circuit 32R / 32L are separated from each other. Becomes

In this way, when the engine stops and the pressure in the charge circuit 32c drops, the charge circuit 32c and the main circuits 32R and 32L communicate with each other by the open / close valve 91, so that the engine operates. Even when the engine is stopped, the pressure in the main circuits 32R and 32L is not closed, and the engine can be started easily.

[0049]

Since the present invention is constructed as described above, it has the following effects. That is, as described in claim 1, in the hydraulic continuously variable transmission that operates the swash plate angle via the hydraulic servo mechanism, the forward side circuit and the reverse side circuit in the main circuit of the hydraulic continuously variable transmission include: A switching valve is provided so that the forward side circuit, the reverse side circuit and the drain circuit can communicate with each other, and the forward side circuit switching valve and the reverse side circuit switching valve are configured as separate switching valves. Since the switching valve is mounted on the oil passage plate on which the main circuit is formed, the switching valve can be switched to the side where the main circuit and the drain circuit are connected when the engine is stopped. Can be released into the housing to which the drain circuit is connected, the closing pressure in the main circuit can be released, the input torque of the HST can be reduced, and the engine can be easily started. Further, since the switching valve provided in the forward circuit and the switching valve provided in the reverse circuit are respectively configured as separate switching valves, only the necessary circuit is opened in the forward-reverse circuit. be able to. In addition, since the switching valve is used to connect the main circuit to the inside of the housing when the engine is stopped, and the switching valve is attached to the oil passage plate, there is no need for external piping and there is no risk of oil leakage. At the same time, noise can be reduced as compared with the case of external piping.

Further, in the hydraulic continuously variable transmission for operating the swash plate angle via the hydraulic servo mechanism as claimed in claim 2, the forward side circuit or the reverse side circuit in the main circuit of the hydraulic type continuously variable transmission is provided. A check / relief valve on one side of the circuit is formed with a throttle portion that connects the main circuit and the charge circuit, and a switching valve is provided on the other side of the forward side circuit or the reverse side circuit to enable communication with the drain circuit. Since it is attached to the oil passage plate on which the main circuit is formed, the number of switching valves provided in the HST can be one, and the cost can be reduced. The check / relief valve of the main circuit on the reverse side may be provided with a throttle hole to secure the neutral position of the movable swash plate. In this case, close the throttle hole to release the pressure. Since it can be used as a diaphragm portion for, it is not necessary to separately form a diaphragm portion,
It is possible to further reduce the cost.

Further, as described in claim 3, the switching valve is linked with an engine starter connected to the hydraulic continuously variable transmission, and the main circuit and the drain circuit communicate with each other when the starter operates. With this configuration, since the switching valve is switched to the side where the main circuit and the drain circuit are connected only when the engine is started, the main circuit and the drain circuit are connected while the working machine is running, etc. It is possible to prevent the erroneous operation of, and reduce the fatigue of the switching valve to improve the durability.

Further, in the hydraulic continuously variable transmission for operating the swash plate angle via the hydraulic servo mechanism, the forward side circuit or the reverse side circuit in the main circuit of the hydraulic type continuously variable transmission is provided. A switching valve is provided on one side of the circuit to enable communication with one of the forward side circuit or the reverse side circuit and the drain circuit, and the switching valve is configured as a 2-position 4-port electromagnetic switching valve to form a main circuit. It was attached to an oil passage plate, and the P port and one of the A port and the B port of the switching valve were connected to one of the forward circuit and the reverse circuit, and the other of the A port and the B port was connected to the drain circuit. So
Since the circuit pressure of the main circuit is not applied to the T port of the switching valve, it is possible to set the circuit pressure of the main circuit without worrying about damage to the switching valve. HST can be configured.

Further, since the throttle part is provided in the middle of the drain circuit as described in claim 5, for example, even when the engine is stopped when the working machine on which the HST is mounted is stopped on a slope. In addition, it is possible to prevent a large amount of hydraulic oil in the main circuit from flowing out, the brake action of the HST is lost, and the working machine to start running, so that reliability can be improved.

Further, since the switching valve is configured as a manual switching valve as described in claim 6, a power source such as a battery for operating the switching valve is not required, so that the power saving and the battery can be achieved. No malfunction occurs due to breakage or the like.

Further, as described in claim 7, in the hydraulic continuously variable transmission which operates the swash plate angle via the hydraulic servo mechanism, an on-off valve that uses the charge pressure as a pilot pressure is provided, and when the charge pressure drops, The open / close valve is opened so that the forward side circuit and the reverse side circuit in the main circuit communicate with each other, and the open / close valve is closed to separate the forward side circuit and the reverse side circuit in the main circuit when the charge pressure rises. Therefore, even when the engine is stopped, the closing pressure of the main circuit can be released, and the engine can be started easily.

Further, as described in claim 8, in the hydraulic continuously variable transmission which operates the swash plate angle via the hydraulic servo mechanism, an opening / closing valve that uses the charge pressure as the pilot pressure is provided, and when the charge pressure decreases, Since the opening / closing valve opens the charge relief valve provided between the main circuit and the charge circuit so that the main circuit and the charge circuit communicate with each other, the pressure of the main circuit is reduced even when the engine is stopped. Is never closed,
The engine can be started easily.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a hydraulic continuously variable transmission including a circuit pressure closing prevention mechanism of the present invention.

FIG. 2 is a front sectional view showing an oil passage plate of the hydraulic continuously variable transmission.

FIG. 3 is a side sectional view showing a check / relief valve.

FIG. 4 is a side sectional view showing a switching valve configured in a two-position two-port type.

FIG. 5 is a circuit diagram showing a second embodiment of a hydraulic continuously variable transmission including a circuit pressure closing prevention mechanism.

6 is a front sectional view showing an oil passage plate of the hydraulic continuously variable transmission shown in FIG.

FIG. 7 is a circuit diagram showing a third embodiment of a hydraulic continuously variable transmission including a circuit pressure closing prevention mechanism.

8 is a front sectional view showing an oil passage plate of the hydraulic continuously variable transmission in FIG.

FIG. 9 is a side sectional view showing a switching valve configured in a 2-position 4-port type.

FIG. 10 is a front cross-sectional view showing an oil passage plate in a hydraulic continuously variable transmission according to a fourth embodiment including a circuit pressure closing prevention mechanism.

FIG. 11 is a front cross-sectional view showing an oil passage plate in a hydraulic continuously variable transmission according to a fifth embodiment including a circuit pressure closing prevention mechanism.

[Explanation of symbols]

10 Hydraulic continuously variable transmission (HST) 11 Switching valve 21c Movable swash plate 31 housing 32R / 32L main circuit 32c charge circuit 32d drain circuit 32f diaphragm 35 Check relief valve 69 Hydraulic servo mechanism

Claims (8)

[Claims] 1. A hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, wherein a switching valve is provided in each of a forward circuit and a reverse circuit in a main circuit of the hydraulic continuously variable transmission. The forward side circuit, the reverse side circuit, and the drain circuit can be communicated with each other, and the forward side circuit switching valve and the reverse side circuit switching valve are configured as separate switching valves. A circuit pressure closing prevention mechanism for a hydraulic continuously variable transmission, which is mounted on an oil passage plate on which a circuit is formed. 2. A check relief valve of one of a forward drive side circuit and a reverse drive side circuit in a main circuit of the hydraulic type continuously variable transmission for operating a swash plate angle via a hydraulic servo mechanism. To form a diaphragm part that connects the main circuit and the charge circuit,
A hydraulic continuously variable transmission characterized in that a switching valve is provided on the other of the forward circuit and the reverse circuit to enable communication with the drain circuit, and the switching valve is mounted on an oil passage plate on which a main circuit is formed. Circuit pressure closure prevention mechanism. 3. The switching valve is interlocked with an engine starter connected to a hydraulic continuously variable transmission so that the main circuit and the drain circuit communicate with each other when the starter operates. The circuit pressure closing prevention mechanism for the hydraulic continuously variable transmission according to claim 1 or 2. 4. A hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, wherein a switching valve is provided in one of a forward circuit and a reverse circuit in a main circuit of the hydraulic continuously variable transmission. By providing one of the forward side circuit or the reverse side circuit and the drain circuit, the switching valve is configured as a 2-position 4-port electromagnetic switching valve and mounted on an oil passage plate on which a main circuit is formed. P of the switching valve
A hydraulic continuously variable transmission characterized in that the port and one of the A port and the B port are connected to one of the forward circuit and the reverse circuit and the other of the A port and the B port is connected to the drain circuit. Circuit pressure closure prevention mechanism. 5. The circuit pressure closing prevention mechanism for a hydraulic continuously variable transmission according to claim 1, wherein a throttle portion is provided at an intermediate portion of the drain circuit. 6. The circuit pressure closing prevention mechanism for a hydraulic continuously variable transmission according to claim 1, wherein the switching valve is a manual switching valve. 7. A hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, wherein an on-off valve that uses a charge pressure as a pilot pressure is provided.
When the charge pressure decreases, the on-off valve opens to communicate the forward side circuit and the reverse side circuit in the main circuit, and when the charge pressure increases, the open / close valve closes to disconnect the forward side circuit and the reverse side circuit in the main circuit. A circuit pressure trapping prevention mechanism for a hydraulic continuously variable transmission characterized in that: 8. A hydraulic continuously variable transmission that operates a swash plate angle via a hydraulic servo mechanism, wherein an on-off valve that uses charge pressure as pilot pressure is provided.
When the charge pressure is reduced, a check relief valve provided between the main circuit and the charge circuit is opened by the opening / closing valve so that the main circuit and the charge circuit are communicated with each other. Mechanism to prevent the circuit pressure from closing in the transmission.