JP2000074185A - Hydrostatic transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrostatic transmission device which can avoid degradation of the transmitting efficiency by introducing such a structure that the characteristics including continuous variable speed change are maintained in the low speed running and the drive force of a power source is transmitted directly to a hydraulic motor in the high speed running. SOLUTION: A hydraulic motor 3 is set to the first or second speed position automatically through a control valve 10 which is changed over in compliance with the pressure of a forward running line 2. When the swash plate inclining angle of a variable discharge pump 1 is made over the set angle in the condition that the hydraulic motor 3 is set to the second speed position, a clutch 16 is engaged to put the hydraulic motor 3 in direct coupling with the engine E, and the motor 3 is driven by the engine E, while in any other cases, the hydraulic motor 3 is driven by the discharged fluid of the pump 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic transmission device used as a drive mechanism for a working vehicle such as a road roller.

[0002]

2. Description of the Related Art Although not specifically shown, a hydrostatic transmission device has a closed circuit constituted by a variable discharge pump and a hydraulic motor. That is, when the variable discharge pump is rotated by the driving force of the engine, the variable discharge pump discharges the hydraulic oil according to the inclination of the swash plate. Then, the hydraulic oil is rotated by the discharged oil to drive the vehicle, and the hydraulic oil discharged from the hydraulic motor is returned to the variable discharge pump.

[0003] In such a hydrostatic transmission device, if the engine speed is kept constant, the variable discharge pump also rotates at a constant speed. Then, in this state, if the swash plate of the variable discharge pump is tilted to control the discharge amount from the minimum to the maximum, the rotation speed of the hydraulic motor can be continuously controlled. Therefore, stepless speed change is possible, and for example, smooth start, acceleration, and deceleration can be realized. Further, if the inclination of the swash plate of the variable discharge pump is reversed, the discharge direction can be reversed. Therefore, the hydraulic motor can be rotated in both the forward and reverse directions to cause the vehicle to travel forward or to travel backward.

[0004]

In such a hydrostatic transmission device as described above, a characteristic such as a stepless speed change becomes very effective especially at a low speed running where the speed is often changed. However, since the driving force of the engine is transmitted to the hydraulic motor side indirectly via the hydraulic oil instead of directly, the transmission efficiency is poor, and the fuel efficiency is inferior. When the vehicle normally travels at high speed, there is almost no need for shifting. for that reason,
At the time of high-speed running, a drawback that transmission efficiency is worse than a characteristic such as a stepless shift is conspicuous, and this drawback becomes a serious problem. An object of the present invention is to maintain the characteristics of stepless shifting during low-speed running, but to transmit the driving force of the power source directly to the hydraulic motor side during high-speed running, thereby reducing the transmission efficiency. It is to provide a hydrostatic transmission device that can be avoided.

[0005]

According to a first aspect of the present invention, there is provided a variable discharge pump which is connected to a power source which rotates in one direction and changes a discharge amount and a discharge direction in accordance with the inclination of a swash plate. A fluid motor driven by the discharge fluid of the variable discharge pump and having two large and small capacities set according to the inclination of the swash plate; and one port of the variable discharge pump A forward travel line connected to one port of the motor, a reverse travel line connecting the other port of the variable discharge pump to the other port of the hydraulic motor, and a communication between the forward travel line and the reverse travel line. A bypass line that bypasses the fluid pressure motor, a communication valve that communicates or shuts off the bypass line, and a capacity switching mechanism that switches the inclination of the swash plate of the fluid pressure motor. A displacement control valve that switches when the pressure of the forward traveling line becomes equal to or higher than a set pressure and switches the displacement switching mechanism to a large displacement side, an on-off valve that switches in conjunction with the displacement control valve, and a fluid pressure motor A clutch for linking or disconnecting the power source to the power source side, a clutch link mechanism that operates on the fluid pressure to act on the clutch to link the fluid pressure motor to the power source side, and a clutch link. A control pump that supplies fluid to the mechanism, a tilt angle detection valve that switches when the tilt angle of the swash plate of the variable discharge pump becomes a tilt angle equal to or greater than a set angle within the forward traveling range of the vehicle, A first branch line connecting the control pump and a pilot chamber of the communication valve via the tilt angle detection valve and the on-off valve;
A second branch line that connects the control pump and the clutch linkage mechanism via the tilt angle detection valve and the on-off valve.

When the pressure of the forward traveling line is lower than the set pressure, the displacement control valve keeps the displacement switching mechanism on the small displacement side and the open / close valve is in the open position. When the swash plate of the pump is tilted beyond a set angle within the forward traveling range of the vehicle, the tilt angle detection valve switches to the open position, and fluid is supplied from the control pump to the first and second branch lines, It is characterized in that the clutch link mechanism is operated to link the clutch, and the communication valve is switched to the open position to connect the bypass line.

According to a second aspect of the present invention, there is provided a communication line connecting the forward traveling line and the reverse traveling line, and a discharge port of a control pump is connected to a connection on the communication line. On the forward traveling line side from the connection portion, a check valve that allows only the flow from the connection portion to the forward traveling line is provided, and on the communication line and on the reverse traveling line side from the connection portion, from the connection portion. It is characterized in that a check valve that allows only the flow to the reverse traveling line is provided.

[0008]

FIG. 1 shows an embodiment of a hydrostatic transmission device according to the present invention. In this device, the variable discharge pump 1 is linked to an engine E which is a power source thereof. And this variable discharge pump 1
Is connected to one port 3 a of the hydraulic motor 3 via the forward traveling line 2. Further, the other port 1b of the variable discharge pump 1 is connected to the other port 3b of the hydraulic motor 3 via the reverse traveling line 4. Therefore, the variable discharge pump 1 and the hydraulic motor 3 form a closed circuit.

The variable discharge pump 1 always rotates in the direction of rotation of the engine E. If the swash plate of the variable discharge pump 1 is tilted in the forward traveling range, the variable discharge pump 1 discharges hydraulic oil from the port 1a to the forward traveling line 2 side. Therefore, the hydraulic motor 3 rotates forward,
Move the vehicle forward. At this time, the vehicle speed is determined according to the tilt angle of the swash plate of the variable discharge pump 1. In other words, the larger the tilt angle, the higher the vehicle speed,
Conversely, reducing the tilt angle decreases the vehicle speed. If the swash plate of the variable discharge pump 1 is tilted in the reverse traveling range, the discharge direction of the variable discharge pump 1 is reversed,
The hydraulic oil is discharged from the port 1b to the reverse traveling line 4 side. Therefore, the hydraulic motor 3 rotates in the reverse direction, causing the vehicle to travel backward.

Further, a control pump 6 is connected to the variable discharge pump 1. The control pump 6 rotates integrally with the variable discharge pump 1 and has a discharge port 6
A constant flow rate is discharged from a. The swash plate of the variable discharge pump 1 as described above is associated with a tilt angle detection valve 5 that switches according to the tilt of the swash plate. When the tilt angle of the swash plate of the variable discharge pump 1 is smaller than the set angle, the tilt angle detection valve 5 maintains the illustrated normal position by the spring 5a. When the tilt angle becomes equal to or larger than the set angle, the port is switched to an open position for communicating the ports 5b and 5c. The port 5b is connected to the control pump 6, and the port 5c is connected to the control line L. Therefore, when the tilt angle of the swash plate of the variable discharge pump 1 becomes equal to or larger than the set angle, the discharge oil of the control pump 6 is supplied to the control line L. The control line L, via an on-off valve 18 to be described later, are connected to a first branch line L ₁ and the second branch line L _2.

Also, between the two traveling lines 2 and 4,
A bypass line 7 that bypasses the hydraulic motor 3 is provided, and a communication valve 8 is provided in the bypass line 7. The pilot chamber 8 of the communication valve 8
b is in communication with the said first branch line L _1. Therefore, on condition that the on-off valve 18 and the tilt angle detection valve 5 are open, the control line L communicates, and the pilot pressure from the control pump 6 is guided to the pilot chamber 8b. However, if the tilt angle detection valve 5 and the opening / closing valve 18 are in the closed position, the pilot pressure is not guided to the pilot chamber 8b, so that the communication valve 8 moves the illustrated normal position, that is, the closed position, by the action of the spring 8a. keep.

When the communication valve 8 is switched to the open position, the bypass line 7 is opened and the variable discharge pump 1 is opened.
Is directly returned to the variable discharge pump 1 via the bypass line 7. Therefore, the discharge oil of the variable discharge pump 1 is not supplied to the hydraulic motor 3, and the variable discharge pump 1 idles. On the other hand, the hydraulic motor 3 is a two-speed motor capable of changing the inclination of the swash plate in two stages and setting its capacity to two types, large and small. In the apparatus of this embodiment, the cylinder 9 is used as a capacity switching mechanism for switching the capacity according to the inclination of the swash plate of the hydraulic motor 3. That is, when the cylinder 9 is in the extended state shown in the figure, the piston rod 9a pushes the swash plate to keep the tilt angle to a minimum. When the cylinder 9 is in the contracted state, the tilt angle of the hydraulic motor 3 is kept at the maximum.

When the tilt angle of the hydraulic motor 3 is small, the torque is small, and when the tilt angle is large, the torque is large. In addition, the variable discharge pump 1
Is constant, the hydraulic motor 3 has low torque and high rotation when the tilt angle is small, and has high torque and low rotation when the tilt angle is large. Therefore, when the displacement angle of the hydraulic motor 3 is small and the displacement is small, the so-called second speed state is achieved, and when the displacement angle is large and the displacement is large, the so-called first speed state is achieved.

However, in this hydrostatic transmission device, the rotation speed of the hydraulic motor 3 is
Since it depends on the discharge amount of the variable discharge pump 1, the first speed is the first speed, and the speed can be controlled within the allowable control range of the tilt angle. The second speed is the second speed and the second speed is the same. Speed control within the allowable control range becomes possible. Therefore, this embodiment is characterized in that the range of speed control in first speed or second speed is increased.

As described above, the cylinder 9 for controlling the tilt angle of the hydraulic motor 3 is provided with a hydraulic chamber 9b and a spring chamber 9c.
d is provided. Therefore, normally, the cylinder 9 is maintained in the contracted state and set to the first speed state by the action of the spring 9d. Then, while the hydraulic pressure is acting on the hydraulic chamber 9b, the cylinder 9 maintains the extended state against the spring 9d. That is, the spring 9d is provided in the hydraulic chamber 9b.
If the hydraulic pressure that overcomes the spring force of
And the hydraulic motor 3 is set to the second speed state.

The hydraulic chamber 9b of the cylinder 9 as described above
Is connected to the port 10a of the first displacement control valve 10. The first displacement control valve 10 includes a spring 1
The normal position shown in the figure is maintained by 0b, and switching is performed when pressure acts on the pilot chamber 10c. The port 10 d is the bypass line 7, and is connected to the branch point 12 on the forward traveling line 2 side from the communication valve 8. The branch point 12 is connected to the first displacement control valve 10.
Is also connected to the pilot room 10c. That is, the first displacement control valve 10 is switched by the pressure of the forward traveling line 2. The first displacement control valve 10
Is the displacement control valve of the present invention.

When the first displacement control valve 10 is in the normal state shown in the figure, the ports 10a and 10d communicate with each other, and the pressure oil from the bypass line 7 is supplied to the hydraulic chamber 9b.
Therefore, the cylinder 9 is extended, and the hydraulic motor 3 is set to the second speed. However, the spring force of the spring 10b is set so that the first displacement control valve 10 does not switch at the pressure of the forward traveling line 2 during the second speed traveling. That is, during the second speed travel, the cylinder 9 maintains the extended state against the spring 9d, but the first displacement control valve 10 keeps the illustrated normal position.

On the other hand, when the pressure of the forward traveling line 2 increases and the pressure overcoming the spring force of the spring 10b acts on the pilot chamber 10c, the first displacement control valve 10 switches to the offset position. First displacement control valve 10
Is switched from the normal position to the offset position, the hydraulic chamber 9b communicates with the tank T via the port 10a. Therefore, the cylinder 9 is contracted by the spring force of the spring 9d, and the hydraulic motor 3 is set to the first speed state.

As is apparent from the above, the hydraulic motor 3 is set to the first speed or the second speed depending on the switching position of the first displacement control valve 10. The first displacement control valve 10 is controlled by the pressure of the forward traveling line 2 acting on the pilot chamber 10c via the bypass line 7. The pressure of the forward traveling line 2 is
When the pressure exceeds the set pressure, the first displacement control valve 10 is switched against the spring 10b. That is, the hydraulic motor 3 is connected to the forward traveling line 2
When the pressure of the forward traveling line 2 is lower than the set pressure, the second speed is set.
Set to speed.

The pressure in the forward traveling line 2 varies depending on the traveling state of the vehicle. For example, when the vehicle is traveling on level ground and no load is applied, the pressure is low. Conversely, when the vehicle is starting or climbing a hill, the pressure of the forward traveling line 2 increases. In other words, when low pressure acts on the pilot chamber 10c, low torque is sufficient, and when high pressure is applied, high torque is required. Therefore, the first displacement control valve 10
When a pressure lower than the set pressure is acting on the pilot chamber 10c by the
Is maintained at the second speed, which is a low torque. On the other hand, when the forward traveling line 2 has a pressure higher than the set pressure,
The first displacement control valve 10 is switched from the illustrated normal position to the offset position. That is, depending on the pressure of the forward traveling line 2, the hydraulic motor 3
First speed and second speed are automatically set.

The hydraulic chamber 9b of the cylinder 9 has a second
The port 11a of the capacity control valve 11 is also connected. The second displacement control valve 11 is connected to the first displacement control valve 10.
It operates in exactly the same way as the above. That is, the normal position shown in the figure is maintained by the spring 11b, and switching is performed when a pressure equal to or higher than the set pressure acts on the pilot chamber 11c. A branch point 13 of the bypass line 7 is connected to the pilot chamber 11c, and the pressure of the reverse traveling line 4 acts via the bypass line 7. When the vehicle is traveling in reverse, the reverse traveling line 4 depends on the traveling state of the vehicle.
Pressure changes. Therefore, during reverse travel, the second displacement control valve 11 operates according to the pressure of the reverse travel line 4, and the first speed and the second speed are automatically set to the hydraulic motor 3. Reference numeral 14 in the figure denotes a damper orifice, which absorbs a shock when the pressure of the forward traveling line 2 or the reverse traveling line 4 changes suddenly.

Further, in this embodiment, unlike the conventional hydrostatic transmission device, the hydraulic motor 3 is linked to the variable discharge pump 1 via a shaft 15 and a clutch 16. Although not specifically shown, the clutch 16 employs a friction clutch system, and usually the hydraulic motor 3 is connected to the variable discharge pump 1.
It is in a shut-off state to shut off from the side. When the clutch 16 is switched to the linked state, the hydraulic motor 3 is mechanically linked to the variable discharge pump 1 so that the driving force of the engine E is directly transmitted to the hydraulic motor 3 via the shaft 15. I have to.

The clutch 16 as described above is operated by a clutch linkage 17 which is operated by hydraulic pressure. The clutch linkage mechanism 17, the second branch line L ₂ and the control line L, which connects the discharge port 6a of the control pump 6. Therefore, if the control line L communicates, the clutch linkage mechanism 1
7 is supplied with pressure oil from the control pump 6, which acts as an operating force, and the clutch linking mechanism 17 links the clutch 16. If the control line L is interrupted,
The clutch linking mechanism 17 maintains the operating force released state.

Further, on the control line L, the tilt angle detecting valve 5 and the on-off valve 18 are provided in series. The opening / closing valve 18 is a valve that operates in conjunction with the first displacement control valve 10. When the first displacement control valve 10 is in the normal position, that is, when the hydraulic motor 3 is set to the second speed, It is in the open position shown.
Conversely, when the first displacement control valve 10 switches and the hydraulic motor 3 is set to the first speed, the on-off valve 18 switches to the closed position.

Therefore, the control line L communicates only when the following two conditions are satisfied. The first condition is that when the pressure of the forward traveling line 2 is lower than the set pressure and the on-off valve 18 is in the open position, that is, when the hydraulic motor 3
Is set to the second speed. The second condition is when the variable discharge pump 1 is tilted at a set angle or more in the forward traveling range. When these two conditions are satisfied at the same time, the second line is connected via the control line L.
Branch line L ₂ and the control pump 6 communicates, actuates the clutch linkage mechanism 17. The set angle is a maximum tilt angle of the swash plate of the variable discharge pump 1 or a tilt angle close thereto. That is, when the vehicle has almost reached the maximum speed, the clutch linkage mechanism 17 is operated, and the hydraulic motor 3 is directly driven by the engine E.

When the above two conditions are satisfied,
The first through the branch line L _1, from the control pump 6,
Pilot pressure acts on the pilot chamber 8b of the communication valve 8. That is, when the hydraulic motor 3 is set to the second speed and the tilt angle detection valve 5 detects a tilt angle greater than the set angle in the forward traveling range, the pilot chamber 8b
And the communication valve 8 is switched to the open position. That is, the bypass line 7 is communicated under the same conditions as the operation of the clutch linkage mechanism 17 described above.

Further, between the two traveling lines 2 and 4,
A communication line 19 is provided. This communication line 19
It is connected to the discharge port 6a of the control pump 6 via the connection section 20. A check valve 21 is provided on the communication line 19 and on the forward traveling line 2 side from the connection portion 20.
Is provided. The check valve 21 is connected to the connecting portion 20.
From the vehicle to the forward traveling line 2 only. on the other hand,
A check valve 22 is provided on the communication line 19 and also on the reverse traveling line 4 side from the connection portion 20. The check valve 22 allows only the flow from the connection portion 20 to the reverse traveling line 4 side. Such a communication line 1
9, the variable discharge pump 1 → the forward traveling line 2
The oil can be replenished from the control pump 6 when the oil leaks from the closed circuit consisting of the hydraulic motor 3 and the reverse traveling line 4 and the amount of oil is reduced.

Next, the operation of the hydrostatic transmission of this embodiment will be described. In a work vehicle such as a load roller, the rotation speed of the engine E is kept constant, and an operation lever (not shown) is moved to operate the swash plate of the variable discharge pump 1. First, the case where the swash plate of the variable discharge pump 1 is tilted in the forward traveling range of the vehicle will be described. In the forward traveling range of the vehicle, as described above, the variable discharge pump 1 discharges the operating oil to the forward traveling line 2 to rotate the hydraulic motor 3 forward.

A description will be given of a case where the pressure of the forward traveling line 2 is lower than the set pressure during the forward traveling as described above. If the pressure of the forward traveling line 2 is lower than the set pressure, the first displacement control valve 10 holds the illustrated normal position by the spring 10b even if the pressure acts on the pilot chamber 10c. In this state, the ports 10a and 10d of the first displacement control valve 10 communicate with each other, and the hydraulic chamber 9 of the cylinder 9 is connected from the bypass line 7 through the port 10a.
Oil pressure is led to b. Then, the cylinder 9 is extended by the pressure action. When the cylinder 9 is extended, the tilt angle of the hydraulic motor 3 is reduced, and the state of the second speed is maintained.
At this time, the on-off valve 18 is in the open position.

In this state, if the tilt angle of the variable discharge pump 1 is within the set angle, the tilt angle detection valve 5 connects the control line L to the tank T via the port 5c, and the second branch line between L ₂ and the control pump 6 remains blocked. If during the second branch line L ₂ and the control pump 6 is interrupted, a clutch linkage mechanism 17, since the operating force releasing state, the clutch 16 is cut off. At the same time, since the first branch line L ₁ also cutoff state, communicating valve 8 also keeps the closed position. Therefore, the hydraulic motor 3 is rotated by the discharge oil of the variable discharge pump 1, and the vehicle runs at the second speed. The running speed of the vehicle at this time is controlled by the tilt angle of the variable discharge pump 1.

As described above, if the speed of the variable discharge pump 1 is increased while increasing the tilt angle during the second speed running, the tilt angle becomes greater than or equal to the set angle in the process. When the tilt angle becomes equal to or larger than the set angle, the tilt angle detection valve 5 is switched to connect the ports 5b and 5c. In this way, when traveling in the second gear,
When the tilt angle of the variable discharge pump 1 is equal to or greater than the set angle, in other words, when the traveling speed of the vehicle is equal to or greater than the set speed, the tilt angle detection valve 5 and the on-off valve 18 are opened, and The two branch line L ₂ is connected to the control pump 6.

[0032] If the second branch line L ₂ to the control pump 6 is connected, the control pump 6 oil discharged clutch linkage mechanism 17
Supplied to Therefore, the clutch linking mechanism 17 operates to link the clutch 16. At the same time,
Also the connection control pump 6 to the first branch line L _1, pressure oil is supplied to the pilot chamber 8b, switch the communication valve 8 in the open position. Therefore, the hydraulic motor 3 is directly connected to the engine E via the clutch 16. Also,
At this time, the discharge oil of the variable discharge pump 1 is returned to the variable discharge pump 1 directly through the bypass line 7 without being supplied to the hydraulic motor 3.

As described above, when the swash plate of the variable discharge pump 1 is tilted at a predetermined angle or more while the hydraulic motor 3 is set to the second speed, that is, during high-speed running, the clutch 16 can be switched to the linked state. it can. Therefore, the driving force of the engine E is directly transmitted to the hydraulic motor 3 via the shaft 15, and the driving force of the engine E can be transmitted to the output side most efficiently. When the bypass line 7 communicates, the two traveling lines 2,
4 has the same pressure, and the hydraulic motor 3 is not rotated by the discharge oil of the variable discharge pump 1, so that there is no possibility that the transmission efficiency is impaired there.

Next, a case where the traveling condition of the vehicle changes and the pressure of the forward traveling line 2 becomes equal to or higher than the set pressure will be described. When a pressure equal to or higher than the set pressure acts on the pilot chamber 10c of the first displacement control valve 10, the first displacement control valve 10 switches from the illustrated normal position to the offset position. Therefore, the hydraulic chamber 9b of the cylinder 9 communicates with the tank T via the port 10a. When the hydraulic chamber 9b communicates with the tank T, the cylinder 9 is contracted by the action of the spring 9d, and the hydraulic motor 3 is set to the first speed.
As described above, when the first displacement control valve 10 is switched to the offset position, the on-off valve 18 is in the closed position. At this time, the second branch line L ₂ Since the connection to the tank T, the clutch linkage mechanism 17 is an operation force releasing state, to cut off the clutch 16. At this time, the communication valve 8 is also in the closed position. When the communication valve 8 is in the closed position in this way, the discharge oil of the variable discharge pump 1
, The hydraulic motor 3 operates at a high torque as described above, and causes the vehicle to run at the first speed. The running speed of the vehicle at this time is controlled by the tilt angle of the variable discharge pump 1, similarly to the case of the second speed.

When oil leaks from the closed circuit as described above, the control pump 6 sends the communication line 1
9 to the forward travel line 2 or the reverse travel line 4. For example, when the pressure of the forward traveling line 2 becomes low due to oil leakage during traveling, oil is supplied via the check valve 21. Conversely, when the pressure of the reverse traveling line 4 becomes lower than the pressure of the connection portion 20 of the communication line 19, the check valve 2
2, oil is supplied from the control pump 6 to the reverse travel line 4.

If oil in the closed circuit leaks and the pressure is kept low, the transmission of power from the variable discharge pump 1 to the hydraulic motor 3 may not be performed properly. When the replenishment is performed from the control pump 6 as described above, the required amount of oil always flows in the closed circuit, and stable operation can be performed. In the above-described embodiment, the control pump 6 used for controlling the clutch link mechanism 17 and switching the communication valve 8 when supplying the leaked oil is shared. In this way, it is economical because separate pumps are not prepared for each purpose but shared.

When the vehicle travels backward, the second
The displacement control valve 11 switches according to the pressure of the reverse travel line 4 as in the case of forward travel, and sets the first speed and the second speed of the hydraulic motor 3. However, within the reverse driving range,
No matter how much the swash plate of the variable discharge pump 1 is tilted, the tilt angle detection valve 5 does not switch. Therefore, the control line L does not communicate. That is, it is unlikely that the vehicle will run at a high speed during reverse travel, and there is almost no need to directly rotate the hydraulic motor 3 with the driving force of the engine E. Therefore, when the swash plate of the variable discharge pump 1 is tilted in the reverse traveling range of the vehicle, the clutch 16 is always kept disconnected. Further, in this embodiment, the control pump 6 is connected to the variable discharge pump 1, but it is not always necessary to connect the control pump 6 to the variable discharge pump 1. However, if it is connected to the variable discharge pump 1, the engine E can be used as a common power source for both pumps.

[0038]

According to the first aspect of the invention, when the hydraulic motor is set to a large capacity, or when the swash plate of the variable discharge pump is tilted within a range not reaching the set angle, even when the capacity is small, During low-speed running, the clutch is in the disengaged state. Therefore, when the vehicle runs at low speed, it functions as a normal hydrostatic transmission device, can continuously control the rotation speed of the hydraulic motor, and can perform stepless speed change. On the other hand, when the fluid pressure motor is set to a small capacity and the swash plate of the variable discharge pump is tilted beyond the set angle in the forward traveling range of the vehicle, that is, at high speed traveling, the clutch is switched to the linked state. , The driving force of the power source can be directly transmitted to the fluid pressure motor side.

When the vehicle travels at high speed, the communication valve is switched to the open position, and the bypass line communicates. Therefore, both traveling lines have the same pressure, and the fluid discharged from the variable discharge pump does not rotate the fluid pressure motor. Therefore, there is no possibility that transmission efficiency is impaired. Further, by using a two-speed motor whose capacity can be set in two stages as the fluid pressure motor, it is possible to control the speed in high torque and low torque, respectively. Further, the capacity of the fluid pressure motor can be automatically set according to the pressure of the forward traveling line. Moreover, since the operation of the clutch linkage mechanism and the capacity switching mechanism and the control of the valve are performed mechanically,
Less malfunction than when using electricity.

According to the second aspect, when a fluid leaks from both traveling lines, the fluid can be supplemented by the control pump. In addition, it is economical because one control pump can be commonly used to supply the fluid to the two traveling lines, control the clutch linkage mechanism and switch the communication valve.

[Brief description of the drawings]

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

[Explanation of symbols]

E engine 1 variable discharge pump 2 forward travel line 3 hydraulic motor 4 reverse travel line 5 tilt angle detection valve 6 control pump 6a discharge port 7 bypass line 8 communication valve 9 cylinder 10 first displacement control valve 15 shaft 16 clutch 17 clutch linkage Mechanism 18 On-off valve 19 Communication line 20 Connection part 21, 22 Check valve L Control line L ₁ First branch line L ₂ Second branch line

Claims (2)

[Claims] 1. A power source that rotates in one direction, a variable discharge pump that is linked to the power source, and that changes a discharge amount and a discharge direction according to a tilt of a swash plate, and that is driven by a discharge fluid of the variable discharge pump. And a hydraulic motor in which two types of large and small displacements are set according to the inclination of the swash plate, and a forward traveling line connecting one port of the variable discharge pump to one port of the hydraulic motor. A reverse traveling line connecting the other port of the variable discharge pump to the other port of the hydraulic motor, a bypass line communicating the forward traveling line and the reverse traveling line and bypassing the hydraulic motor, A communication valve for communicating or blocking the bypass line; a capacity switching mechanism for switching the inclination of the swash plate of the fluid pressure motor; and It is switched when it becomes the above, a capacity control valve for switching the capacity switching mechanism to the large capacity side, an on-off valve for switching in conjunction with the capacity control valve, and a fluid pressure motor linked to the power source side. A clutch that disconnects the linkage, a clutch linkage that operates on the hydraulic pressure to act on the clutch to link the fluid pressure motor to the power source side, and a control pump that supplies fluid to the clutch linkage. A tilt angle detection valve that switches when the tilt angle of the swash plate of the variable discharge pump becomes equal to or greater than a set angle within a forward traveling range of the vehicle; and a pilot for the control pump and the communication valve. A first branch line connecting the chamber with the tilt angle detection valve and the on-off valve, and the control pump and the clutch linkage mechanism are connected to the tilt angle detection valve and the A second branch line connected via a valve closing mechanism. When the pressure of the forward traveling line is lower than a set pressure, the capacity control valve maintains the capacity switching mechanism on the small capacity side and opens and closes the on-off valve. Position, and in this state, when the swash plate of the variable discharge pump is tilted at a set angle or more within the forward traveling range of the vehicle,
The tilt angle detection valve is switched to the open position, fluid is supplied from the control pump to the first and second branch lines, a clutch linkage mechanism is operated to link the clutch, and the communication valve is opened to the open position. A hydrostatic transmission device configured to switch to and communicate with the bypass line. 2. A communication line for connecting a forward traveling line and a reverse traveling line is provided, and a discharge port of a control pump is connected to a connection on the communication line. On the traveling line side, a check valve that allows only the flow from the connection portion to the forward traveling line is provided, and on the communication line and on the reverse traveling line side from the connection portion, from the connection portion to the reverse traveling line. 2. The hydrostatic transmission device according to claim 1, further comprising a check valve that allows only the flow of the fluid.