JP2000074183A - 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: When the swash plate inclining angle of a variable discharge pump 1 is made over the set angle in the condition that a hydraulic motor 3 is set to the second speed position, a clutch 12 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 arrangement is allowed to work as a usual hydrostatic transmission device whereby 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 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 the inclination of a swash plate. A fluid pressure 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 connected to the fluid pressure motor A forward running line connected to one port, a reverse running line connecting the other port of the variable discharge pump to the other port of the fluid pressure motor, and a fluid connected to the forward running line and the reverse running line. A bypass line that bypasses the pressure motor, a communication valve that communicates or shuts off the bypass line, and a fluid pressure motor that is linked to the power source side or that linkage is shut off Clutch, a clutch switching mechanism that acts on the clutch to link the fluid pressure motor to the power source side, a capacity selection mechanism that selects the capacity of the fluid pressure motor, and a fluid pressure mechanism that is selected according to the capacity selection mechanism. A capacity switching mechanism for switching the inclination of the swash plate of the motor,
A tilt angle detecting mechanism for detecting a tilt angle of a swash plate of the variable discharge pump, wherein the displacement selecting mechanism selects a small capacity of a fluid pressure motor, and the tilt angle detecting mechanism is a vehicle. When a tilt angle equal to or larger than the set angle is detected within the forward traveling range, the clutch switching mechanism connects the clutch, and the communication valve connects the bypass line.

According to a second aspect of the present invention, a clutch switching mechanism is linked to a clutch, and supplies a fluid to the clutch linkage when the clutch control valve is switched over. An electric tilt angle sensor for detecting the tilt angle of the variable discharge pump, and a clutch control valve or a control valve according to the detection signal of the tilt angle sensor and the selection signal of the displacement selection mechanism. A controller for controlling the communication valve, the controller comprising a selection signal for selecting a small displacement of the fluid pressure motor from the displacement selection mechanism, and a setting angle within a forward traveling range of the vehicle from the tilt angle sensor. When the detection signals for detecting the above tilt angles are simultaneously input, the controller causes the clutch control valve and the communication valve to communicate with each other. Rikae Te, together to supply the fluid from the control pump to the clutch linkage mechanism has a feature in that a configuration for communicating the bypass line.

According to a third aspect of the present invention, there is provided a clutch link mechanism in which a clutch switching mechanism is linked to a clutch and operated by fluid pressure, a control pump for supplying fluid to the clutch link mechanism,
A first control line connecting the control pump and the clutch linkage mechanism, and a communication position when the tilt angle of the swash plate of the variable discharge pump is greater than or equal to a set angle within a forward traveling range of the vehicle; And a second control line connecting the first control line and the pilot port of the communication valve, the second control line comprising a clutch control valve provided in series with the tilt angle detection valve. When the small capacity is selected by the capacity selection mechanism, the clutch control valve is switched to the communication position. In this state, when the tilt angle detection valve is switched to the communication position, the first control line and the second control line are connected to each other. It is characterized in that fluid is supplied from a control pump to the control line, the clutch is linked, and the bypass line is linked.

According to a fourth aspect of the present invention, there is provided a communication line connecting a forward traveling line and a reverse traveling line, a connecting portion connecting a discharge port of a control pump on the communicating line, and the connecting line on the communicating line. A check valve provided on the forward traveling line side from the portion and allowing only the flow from the connection portion to the forward traveling line, and a check valve provided on the communication line and on the reverse traveling line side from the connection portion, from the connection portion A check valve that allows only the flow to the reverse traveling line is provided, and the capacity switching mechanism is operated by a fluid supplied from a control pump.

[0009]

FIG. 1 shows a first 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. Then, one port 1 a of the variable discharge pump 1 is connected to one port 3 a of the hydraulic motor 3 via the forward traveling line 2. 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 at a speed corresponding to the discharge amount, and the vehicle travels forward. The maximum discharge amount is obtained when the tilt angle of the swash plate of the variable discharge pump 1 is maximum. If the swash plate of the variable discharge pump 1 is tilted in the reverse travel range, the discharge direction of the variable discharge pump 1 is reversed, and the reverse travel line 4
Discharge hydraulic oil to the side. Therefore, the hydraulic motor 3 rotates in reverse at a speed corresponding to the discharge amount, and the vehicle travels backward.

The swash plate of the variable discharge pump 1 is associated with a tilt angle sensor 5 for detecting the tilt of the swash plate. The tilt angle sensor 5 is an electrical sensor, is connected to the controller C, and inputs a tilt angle detection signal to the controller C. Further, a control pump 6 is connected to the variable discharge pump 1. The control pump 6 rotates together with the variable discharge pump 1 by the driving force of the engine E, and discharges oil from the discharge port 6a. The discharge port 6a of the control pump 6 is connected to the tank T via the relief valve 7.
Connected to.

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 the first embodiment, the cylinder 8 is used as a capacity switching mechanism for switching the capacity according to the inclination of the swash plate of the hydraulic motor 3.
Is used. That is, when the cylinder 8 is in the contracted state shown in the drawing, the tilt angle of the hydraulic motor 3 is kept at the maximum. When the hydraulic motor 3 is extended, the piston rod 8a pushes the swash plate to keep the tilt angle to a minimum.

When the tilt angle of the hydraulic motor 3 is large, the torque increases, and when the tilt angle is small, the torque decreases. If the discharge rate of the variable discharge pump 1 is constant, the hydraulic motor 3 rotates at a low speed when the tilt angle is large, and at a high speed when the tilt angle is small. Therefore, when the tilt angle of the hydraulic motor 3 is large and the capacity is large, the hydraulic motor 3 has a high torque and a low rotation, and is in a so-called first speed state. On the other hand, when the tilt angle is small and the displacement is small, the hydraulic motor 3 has a low torque and a high rotation, and is in a so-called second speed state. However, in this hydrostatic transmission device, the rotation speed of the hydraulic motor 3 is controlled by the variable discharge pump 1
Because it depends on the discharge amount of
High torque and high rotation are possible, and low torque and low rotation are also 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 8 for controlling the tilt angle of the hydraulic motor 3 has a hydraulic chamber 8b and a rod-side chamber 8c, and a spring 8d is provided in the rod-side chamber 8c. Therefore, when the hydraulic pressure is not acting on the hydraulic chamber 8b, the cylinder 8 keeps the illustrated contracted state by the action of the spring 8d. In other words, the hydraulic chamber 8b
, The hydraulic motor 3 is set to the first speed state. When a hydraulic pressure acts on the hydraulic chamber 8b, the cylinder 8 expands against the spring 8d to reduce the tilt angle of the hydraulic motor 3 and set the hydraulic motor 3 to the second speed state.

In the hydraulic chamber 8b of the hydraulic cylinder 8 as described above, a selection valve 9 which is a capacity selection mechanism of the present invention is provided.
Are connected. The selection valve 9 is configured such that the valve position is manually switched by a lever 10. When the selection valve 9 is at the normal position in FIG. 1, the hydraulic chamber 8b of the cylinder 8 communicates with the tank T to keep the cylinder 8 in a contracted state. At this time, the hydraulic motor 3 is set to the first speed. On the other hand, when the selection valve 9 is
When the state shown in the drawing is switched to the other position on the lower side in the drawing, the discharge port 6a of the control pump 6 communicates with the hydraulic chamber 8b of the cylinder 8, and hydraulic pressure acts on the hydraulic chamber 8b. When the hydraulic pressure acts on the hydraulic chamber 8b in this manner, the cylinder 8 extends, and the piston rod 8a pushes the swash plate of the hydraulic motor 3 to reduce the tilt angle. Therefore, the hydraulic motor 3 is set to the second speed. As is clear from the above, the hydraulic motor 3 is set to the first speed or the second speed depending on the switching position of the selection valve 9. The controller C is connected to the selection valve 9, and the switching position of the selection valve 9 is input to the controller C. Then, the controller C
Depending on the switching position of the selection valve 9, the hydraulic motor 3
Is set to 1st speed or 2nd speed.

Further, in the first embodiment, unlike the conventional hydrostatic transmission device,
The hydraulic motor 3 is linked to the variable discharge pump 1 via a shaft 11. However, a clutch 12 is provided in the middle of the shaft 11. Although not specifically shown, the clutch 12 employs a friction clutch system.
The hydraulic motor 3 is shut off from the variable discharge pump 1 side. When the clutch 12 is switched to the linked state, the hydraulic motor 3 is 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 11. .

The clutch 12 is operated by a clutch linkage 13 which is operated by hydraulic pressure. A clutch control valve 14 is connected to the clutch linkage mechanism 13. This clutch control valve 1
4 normally maintains the illustrated normal position by the action of the spring 14a. In this normal position, the clutch linking mechanism 13 is linked to the tank T via the port 14b, and keeps the operating force released. If the clutch link mechanism 13 is in the operating force released state, the clutch 12 is disconnected. When the solenoid 14c of the clutch control valve 14 is excited, the clutch control valve 14
4a, the switching position is switched to the switching position on the right side of the drawing.
In this switching position, the ports 14b and 14d communicate with each other, so that the pressure oil from the control pump 6 is guided to the clutch linkage mechanism 13. When pressurized oil is introduced into the clutch linkage 13, it acts as an operating force to produce the clutch 12.
Is linked.

Since the solenoid 14c is connected to the controller C, it is controlled by the controller C to keep the clutch control valve 14 at the normal position or at the switching position. Become. In the first embodiment, the clutch linking mechanism 13 and the clutch control valve 14
And the control pump 6 constitute a clutch switching mechanism of the present invention. Then, when the following condition is satisfied, the controller C excites the solenoid 14c,
The clutch 12 is linked. That is, the selection valve 9
Is switched to the second speed position, and the solenoid 14c is excited when the variable discharge pump 1 is tilted beyond a set angle in the forward traveling range. In other words, when the discharge amount of the variable discharge pump 1 becomes close to the maximum amount and the vehicle moves forward at high speed, the solenoid 14c is excited to drive the hydraulic motor 3 directly by the engine E. .

A bypass line 15 that bypasses the hydraulic motor 3 is provided between the two running lines 2 and 4, and a communication valve 16 is provided in the bypass line 15.
The communication valve 16 maintains a closed position, which is a normal position, by the action of a spring 16a, and switches to an open position by exciting a solenoid 16b.
The solenoid 16b is controlled by an output signal of the controller C. That is, the controller C receives a signal that selects the second speed from the selection valve 9, and
When the tilt angle sensor 5 detects a tilt angle equal to or larger than the set angle in the forward traveling range, the solenoid 16b is excited. That is, the bypass line 15 is communicated under the same conditions as those for switching the clutch control valve 14 described above.

Further, between the two traveling lines 2, 4,
A communication line 17 is provided. The communication line 17 is connected to the discharge port 6 of the control pump 6 through a connection portion 18.
a and the relief valve 7 are connected. A check valve 19 is provided on the communication line 17 and on the forward traveling line 2 side from the connection portion 18. The check valve 19 allows only the flow from the connection portion 18 to the forward traveling line 2. On the other hand, on the communication line 17,
A check valve 20 is also provided on the reverse traveling line 4 side from the connection portion 18. The check valve 20 allows only the flow from the connection portion 18 to the reverse traveling line 4 side. Since such a communication line 17 is provided, when the oil leaks to the outside from the closed circuit consisting of the variable discharge pump 1 → the forward traveling line 2 → the hydraulic motor 3 → the backward traveling line 4, the amount of oil decreases. The oil can be replenished from the control pump 6.

Next, the operation of the hydrostatic transmission of the first 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.

At this time, if the selection valve 9 is held at the normal position shown in the figure, the hydraulic chamber 8b of the cylinder 8 communicates with the tank T. Therefore, the cylinder 8 maintains the contracted state by the action of the spring 8d, and maintains the hydraulic motor 3 in the first speed state. If the selection valve 9 is in the normal state, the controller C determines that the hydraulic motor 3 is in the first speed state.
At this time, the clutch control valve 14
Also holds the illustrated normal position. Therefore, the clutch linking mechanism 13 maintains the operating force released state, and the clutch 1
Leave 2 shut off. At this time, the communication valve 16 also maintains the closed position. Since the communication valve 16 keeps the closed position in this way, the discharge oil of the variable discharge pump 1 is supplied to the hydraulic motor 3, and the hydraulic motor 3 operates at a high torque as described above, causing the vehicle to travel 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.

Next, the selector valve 9 is operated by operating the lever 10.
Is switched to the lower position in the drawing, the hydraulic chamber 8 of the cylinder 8
b communicates with the control pump 6 via the selection valve 9.
Therefore, the hydraulic pressure is guided to the hydraulic chamber 8b, and the cylinder 8 is extended by the pressure action. Cylinder 8
Extends, the tilt angle of the hydraulic motor 3 decreases,
It becomes the state of the 2nd speed. The state of the second speed is input to the controller C via the selection valve 9.

At this time, if the tilt angle of the variable discharge pump 1 detected by the tilt angle sensor 5 is smaller than the set angle, the controller C judges this and keeps the clutch control valve 14 at the normal position shown in the figure. , The clutch 12 is kept disconnected. At the same time, the communication valve 16 also maintains 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, similarly to the case of the first speed.

As described above, when the speed is increased while increasing the tilt angle of the variable discharge pump 1 during the second speed running, the tilt angle becomes larger than the set angle in the process. When the tilt angle becomes equal to or larger than the set angle, the tilt angle sensor 5 detects this and outputs a signal to the controller C. At this time, the controller C
, A second speed signal from the selection valve 9 is also input. As described above, when the tilt angle of the variable discharge pump 1 is equal to or larger than the set angle during the second speed running, in other words, when the running speed of the vehicle is equal to or higher than the set speed, the controller C sets the clutch control valve 14 to operate. Switch to the right position in the drawing.

When the clutch control valve 14 is switched to the right position, the clutch linking mechanism 13 is operated to link the clutch 12. At the same time, the controller C switches the communication valve 16 to the open position. Therefore, the hydraulic motor 3 is connected to the engine E via the clutch 12.
Will be directly connected. At this time, the discharge oil of the variable discharge pump 1 is not supplied to the hydraulic motor 3 but returned to the variable discharge pump 1 through the bypass line 15.

When an oil leak occurs from the closed circuit as described above, the control pump 6 sends the oil to the communication line 1.
The oil can be replenished to the forward travel line 2 or the reverse travel line 4 via. If there is no oil leakage from the closed circuit, the discharge oil of the control pump 6 is returned to the tank T from the connection portion 18 with the communication line 17 via the relief valve 7. Therefore, the set pressure of the relief valve 7 acts on the connection portion 18. In this manner, since the pressure of the connecting portion 18 is maintained, when the pressure of the forward traveling line 2 or the backward traveling line 4 becomes lower than the pressure of the connecting portion 18, oil can be supplied from the communication line 17.

For example, if the pressure of the reverse traveling line 4 becomes lower than the pressure of the connecting portion 18 of the communication line 17 due to oil leakage during traveling, the reverse traveling line is transmitted from the control pump 6 via the check valve 20. Refill 4 with oil. Conversely, when the pressure of the forward traveling line 2 becomes low, the oil is similarly supplied via the check valve 19. If the 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 well, but as described above. If you supply from the control pump 6,
During the closed circuit, a required amount of oil always flows, and stable operation can be performed.

When the vehicle travels backward, it is unlikely that the vehicle will run at high speed. Therefore, 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 inclined in the reverse traveling range of the vehicle, the clutch 12 is always kept disconnected.

FIG. 2 shows a second embodiment of the hydrostatic transmission device according to the present invention. This device controls the clutch switching mechanism and controls the bypass line 1
The fifth embodiment differs from the first embodiment in that the control for communicating the first and second pumps 5 is performed entirely by hydraulic pressure. However, when traveling at low speed, the variable discharge pump 1 driven by the engine E
And the forward traveling line 2, the hydraulic motor 3, and the reverse traveling line 4 form a closed circuit and function as a normal hydrostatic transmission device.
This is the same as the embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.

Hereinafter, a part controlled by the hydraulic pressure in the configuration of the apparatus will be described in detail. The variable discharge pump 1 is provided with a control pump 6 that rotates together with the variable discharge pump 1. In the second embodiment,
The discharge oil of the control pump 6 causes the clutch linkage 13
Or the bypass line 15 is communicated. The discharge port 6a of the control pump 6 has a branch point 2
9 to a first control line 25 connecting the clutch linkage 13. The first control line 25 is provided with a tilt angle detection valve 21 and a first control valve 22.

The tilt angle detecting valve 21 is provided in place of the tilt angle sensor 5 of the first embodiment for detecting the tilt of the swash plate of the variable discharge pump 1. 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 21 maintains the cutoff position shown by the spring 21a. When it exceeds the angle, it switches to the communication position. Further, the first control valve 22 maintains the illustrated shut-off position by the spring 22b, and switches to the communication position when pressure is applied to the pilot port 22a.

The first control line 25 is in communication only after the first control valve 22 and the tilt angle detection valve 21 are both switched to the communication position. When the first control line 25 communicates, the pressure oil of the control pump 6 is supplied to the clutch linkage mechanism 13 to link the clutch 12.
In the second embodiment, the first control valve 22 is the clutch control valve of the present invention, and the clutch linkage mechanism 13, the tilt angle detection valve 21, the first control valve 22,
The control pump 6 constitutes a clutch switching mechanism.

Further, a second control line 26 is provided which connects from a branch point 30 of the first control line 25 to a pilot port 24a of the communication valve 24. The communication valve 2
Reference numeral 4 denotes a valve for connecting or disconnecting the bypass line 15, and the valve 4 is maintained in a shut-off position by a spring 24b. However, when hydraulic pressure is applied to the pilot port 24a, the pilot port 24a is switched to the communication position. When both the first control valve 22 and the tilt angle detection valve 21 are in the communication position at the same time, the pressure oil from the control pump 6 is supplied to the second control line 26, and the communication valve 24 is in the communication position. Switch.

On the other hand, the hydraulic motor 3 is the same as the motor of the first embodiment, and by setting the first speed and the second speed,
High torque and low torque can be set. As a capacity switching mechanism for switching the inclination of the swash plate, a cylinder 8 similar to that of the first embodiment is provided. However, in the second embodiment, the hydraulic chamber 8b of the cylinder 8 is connected to the control pump 6 via the second control valve 23. In the illustrated state, since the hydraulic chamber 8b is connected to the tank T and the cylinder 8 is contracted, the hydraulic motor 3 is set to the first speed. When the second control valve 23 switches to the other valve position, pressure oil is supplied from the control pump 6 to the hydraulic chamber 8b, and the cylinder 8 extends. Then, the hydraulic motor 3 is set to the second speed side. The second control valve 2
The third pilot port 23a is connected to the third control line 27.
Are connected to the control pump 6 via the selection valve 9. Therefore, when the selection valve 9 is switched to the communication position, the second control valve 23 is switched by the pressure oil from the control pump 6.

The selection valve 9 is a valve for selecting the first speed or the second speed by the lever 10 as in the first embodiment. The illustrated shutoff position is a valve position for selecting the first speed, and the communication position is a valve position for selecting the second speed. Further, the third control line 27 is connected to the selection valve 9.
The pilot port 22a of the first control valve 22 is connected via a fourth control line 28 branched from the branch point 31 of the first control valve 22. Therefore, when the selection valve 9 is switched to the communication position in order to select the second speed of the hydraulic motor 3, the first
The control valve 22 switches.

The operation of the device according to the second embodiment will be described below. However, description will be given only for forward running, and description for backward running will be omitted. First, consider the state of FIG. 2 in which the first speed at which the hydraulic motor 3 outputs high torque is selected. In this state, since the selection valve 9 is in the shut-off position, the first control valve 22 is also in the shut-off state. Therefore, even if the swash plate of the variable discharge pump 1 is changed from the minimum angle to the maximum angle, the first control line 25 communicates and the clutch linkage 13 does not operate. That is, the hydraulic motor 3 rotates according to the discharge amount of the variable discharge pump 1.
At this time, the hydraulic motor 3 operates at a high torque,
This is the same as the first embodiment.

Next, when the selection valve 9 is switched, the third and fourth control lines 27 and 28 communicate with the control pump 6, and the first control valve 22 and the second control valve 23 are switched. When the second control valve 23 is switched, the cylinder 8
Extend, and the hydraulic motor 3 is set to the second speed. At this time, the first control valve 22 is in a communication state, but the first and second control lines 25 and 26 and the control pump 6 are kept disconnected until the tilt angle detection valve 21 is in a communication state. Up to. In this state, if the inclination of the swash plate of the variable discharge pump 1 is changed within a range smaller than the set angle, the tilt angle detection valve 21 does not switch. That is, the operation of the hydraulic motor 3 at a low torque is the same as in the first embodiment.

On the other hand, when the swash plate of the variable discharge pump 1 is tilted to the maximum tilt angle, the tilt angle detection valve 21 is switched to the communicating position, and the control pump 6 and the first and second control lines 2 are switched.
Communication between 5 and 26 is simultaneous. When the first control line 25 communicates, the clutch 1 is operated by the clutch linkage mechanism 13.
2 works together. Therefore, the hydraulic motor 3 is linked to the engine E via the clutch 12 and this engine E
Directly driven by As described above, when the swash plate of the variable discharge pump 1 is inclined at a set angle or more with the hydraulic motor 3 set to the second speed, that is, at the time of high-speed traveling,
The clutch 12 can be switched to the linked state. Therefore, the driving force of the engine E is directly transmitted to the hydraulic motor 3 via the shaft 11, and the driving force of the engine E can be transmitted to the output side most efficiently. When the second control line 26 communicates with the control pump 6, the communication valve 24 is switched, and the bypass line 15 is connected. Therefore, both 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.

In the first and second embodiments, the first speed,
The selection valve 9 for selecting the second speed is switched by the lever 10, but this selection valve is used as an electromagnetic valve.
It is also possible to switch by exciting the solenoid. In this case, the valve is switched by turning on / off the manual switch. Although the control pump 6 is connected to the variable discharge pump 1 in the first and second embodiments, 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.

[0041]

According to the first to fourth aspects of the present invention, when the hydraulic motor is set to a large capacity, or even when the capacity is small,
When the swash plate of the variable discharge pump is tilted within a range not reaching the set angle, that is, during low-speed running, the clutch is in the disconnected 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 at a set angle or more in the forward traveling range of the vehicle, that is,
During high-speed running, the clutch is switched to the linked state, so that the driving force of the power source can be directly transmitted to the fluid pressure motor side. Also, during high-speed traveling, the communication valve is switched to the communicating position, and the bypass line communicates, so that both traveling lines have the same pressure, and the fluid motor is not rotated by the discharge fluid of the variable discharge pump,
Therefore, there is no possibility that transmission efficiency is impaired. Furthermore, as a fluid pressure motor, its capacity can be set in two stages.
By using a high-speed motor, high torque and low torque can be selected and speed control in each torque range can be performed.

In particular, according to the third aspect, since the fluid pressure is used as the clutch switching mechanism, there is almost no malfunction and the clutch can be switched reliably. Also,
According to the fourth aspect, when a fluid leaks from both traveling lines, the fluid can be supplemented by the control pump. Moreover, one control pump is shared,
Since the operation of the clutch linking mechanism and the capacity switching mechanism and the supply of fluid to both of the traveling lines can be performed, it is economical.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a hydrostatic transmission device according to a first embodiment.

FIG. 2 is a circuit diagram showing a hydrostatic transmission device according to a second embodiment.

[Explanation of symbols]

 E engine 1 variable discharge pump 2 forward running line 3 hydraulic motor 4 reverse running line 5 tilt angle sensor 6 control pump 6a discharge port 8 cylinder 9 selection valve 10 lever 11 shaft 12 clutch 13 clutch linkage mechanism 14 clutch control valve 15 bypass line 16, 24 communication valve 17 communication line 18 connection 19, 20 check valve 21 tilt angle detection valve 22 first control valve 23 second control valve 25 first control line 26 second control line C controller

Claims (4)

[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 travel line connecting the other port of the variable discharge pump to the other port of the hydraulic motor, a bypass line communicating the forward travel line and the reverse travel line and bypassing the hydraulic motor, A communication valve for connecting and disconnecting a bypass line, a clutch for connecting a fluid pressure motor to the power source side, and disconnecting the connection; , A clutch switching mechanism for linking the fluid pressure motor to the power source side, a capacity selection mechanism for selecting the capacity of the fluid pressure motor, and inclination of the swash plate of the fluid pressure motor in accordance with the selection by the capacity selection mechanism. And a tilt angle detecting mechanism for detecting the tilt angle of the swash plate of the variable discharge pump, wherein the displacement selecting mechanism selects the small displacement of the fluid pressure motor, and When the shift angle detection mechanism detects a tilt angle equal to or greater than a set angle within the forward traveling range of the vehicle, the clutch switching mechanism connects the clutch and the communication valve connects the bypass line. Static transmission device. 2. A clutch switching mechanism, wherein the clutch switching mechanism is linked to a clutch and operated by a fluid pressure, a clutch control valve, and a control pump for supplying a fluid to the clutch link mechanism when the clutch control valve is switched. And an electric tilt angle sensor that detects the tilt angle of the variable discharge pump, and controls the clutch control valve and the communication valve according to the detection signal of the tilt angle sensor and the selection signal of the displacement selection mechanism. A controller that performs a selection signal for selecting a small capacity of the fluid pressure motor from the capacity selection mechanism, and a tilt signal from the tilt angle sensor.
The controller switches between the clutch control valve and the communication valve when the detection signal that has detected the tilt angle equal to or greater than the set angle within the forward traveling range of the vehicle is simultaneously input, and the control pump switches the clutch linkage from the control pump. 2. The hydrostatic transmission device according to claim 1, wherein a fluid is supplied to a mechanism and the bypass line is communicated with the mechanism. 3. A clutch switching mechanism, wherein the clutch switching mechanism is linked to a clutch and operated by a fluid pressure, a control pump for supplying fluid to the clutch linkage, and a control pump for connecting the control pump and the clutch linkage. (1) a control line, a tilt angle detection valve that switches to a communication position when the tilt angle of the swash plate of the variable discharge pump becomes a tilt angle greater than or equal to a set angle within a forward traveling range of the vehicle, and the tilt A clutch control valve provided in series with the angle detection valve, a second control line connecting the first control line and a pilot port of the communication valve, and the clutch is selected when a small capacity is selected by a capacity selection mechanism. When the control valve is switched to the communication position, and in this state, the tilt angle detection valve is switched to the communication position, the control valve switches to the first control line and the second control line. 2. The hydrostatic transmission device according to claim 1, wherein a fluid is supplied from a pump, the clutch is connected, and the bypass line is connected. 4. A communication line connecting the forward traveling line and the reverse traveling line, a connection portion connecting the discharge port of the control pump to the communication line, and traveling forward from the connection portion on the communication line. A check valve provided on the line side and allowing only the flow from the connection portion to the forward travel line; and a check valve provided on the communication line and on the reverse travel line side from the connection portion, from the connection portion to the reverse travel line. 4. The hydrostatic transmission device according to claim 2, further comprising a check valve that allows only flow to the hydraulic pump, and wherein the capacity switching mechanism is operated by a fluid supplied from a control pump.