JP2000046152A - Hydrostatic transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrostatic transmission device that avoids any degradation in transmission efficiency by maintaining a continuously variable transmission gear ratio control characteristic at low vehicle speed and transmitting the driving force of a power source directly to its hydraulic motor at high vehicle speed. SOLUTION: When the swash plate of a variable displacement pump 1 is inclined over a preset angle in a vehicle forward running range, a selector valve 14 is switched to bring a control pump 13 into communication with a clutch mechanism 6 and with a pilot chamber 12 of a communication valve 10. The clutch mechanism 6 is thus engaged to connect a hydraulic motor 3 to a power source, and the communication valve 10 is also switched into its communication position to communicate a communication line 9.

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 displacement pump and a hydraulic motor. That is, when the variable displacement pump is rotated by the driving force of the engine, the variable displacement pump discharges hydraulic oil according to the inclination of the swash plate. Then, the hydraulic motor is rotated by the discharged oil to drive the vehicle,
The hydraulic oil discharged from the hydraulic motor is returned to the variable displacement pump.

[0003] In such a hydrostatic transmission device, if the engine speed is kept constant, the variable displacement pump also rotates at a constant speed. And
In this state, if the swash plate of the variable displacement 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. If the inclination of the swash plate of the variable displacement pump is reversed, the discharge direction can be reversed. Therefore, the vehicle can be made to travel forward or backward by rotating the hydraulic motor in both the forward and reverse directions.

[0004]

In such a hydrostatic transmission device as described above, a characteristic such as a continuously variable transmission becomes very effective especially at a low vehicle speed where the transmission is frequently 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 poor. When the vehicle normally travels at a high vehicle speed, there is almost no need for shifting, and the disadvantage that transmission efficiency is worse than the characteristic of stepless shifting is a serious problem. The purpose of this invention is
At low vehicle speeds, while maintaining characteristics such as stepless shifting, at high vehicle speeds, the driving force of the power source is transmitted directly to the hydraulic motor side, thereby avoiding deterioration in transmission efficiency. It is to provide a hydrostatic transmission device.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a variable displacement pump that is linked to a power source that rotates in one direction and that changes the discharge amount and discharge direction in accordance with the inclination of a swash plate. Hydraulic motor, a forward running line connecting one port of the variable displacement pump to one port of the hydraulic motor, and a reverse running connecting the other port of the variable displacement pump to the other port of the hydraulic motor. It assumes a hydrostatic transmission device with a running line. Then, a clutch mechanism for linking the fluid pressure motor to the power source side or disconnecting the link, and usually keeping the clutch mechanism in a disconnected state, and switching the clutch mechanism to the linked state when a predetermined pressure is introduced. A clutch switching unit, a control pump that rotates together with the variable displacement pump, a communication line that communicates the forward traveling line and the reverse traveling line, and a communication line. When a swash plate of a variable displacement pump and a communication valve that switches to a communication position that communicates with a communication line when a predetermined pressure is guided to the pilot chamber is tilted beyond a set angle in a forward traveling range of the vehicle,
It is characterized in that the control pump communicates with the clutch switching means and the pilot chamber of the communication valve, and a switching valve that guides a predetermined pressure to the clutch switching means and the pilot chamber of the communication valve.

[0006]

FIG. 1 shows an embodiment of a hydrostatic transmission device according to the present invention. The variable displacement pump 1 is linked to an engine E as its power source. Then, one port 1 a of the variable displacement 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 displacement pump 1 is connected to the other port 3b of the hydraulic motor 3 via the reverse traveling line 4. Therefore, the variable displacement pump 1 and the hydraulic motor 3 form a closed circuit.

When the engine E is driven, the variable displacement pump 1 rotates in the direction of rotation of the engine E. Then, as shown in FIG. 1, when the swash plate of the variable displacement pump 1 is tilted in the forward traveling range, the variable displacement pump 1 discharges hydraulic oil from the port 1a to the forward traveling line 2 side. Therefore, the hydraulic motor 3 rotates forward according to the discharge amount, and the vehicle travels forward.
If the swash plate of the variable displacement pump 1 is turned in the opposite direction and tilted in the reverse traveling range, the discharge direction of the variable displacement pump 1 is reversed, and hydraulic oil is discharged from the port 1b to the reverse traveling line 4 side. I do. Therefore, the hydraulic motor 3 rotates in the reverse direction according to the discharge amount, and the vehicle travels backward.

Further, in the first embodiment, unlike the conventional hydrostatic transmission device,
The hydraulic motor 3 is connected to a variable displacement pump 1 via a shaft 5.
It is linked to the side. However, a clutch mechanism 6 is provided in the middle of the shaft 5. Although not specifically shown, a friction clutch system is employed as the clutch mechanism 6, and the hydraulic motor 3 is linked to the variable displacement pump 1 or the link is cut off.

The clutch mechanism 6 is switched by the cylinder 7. That is, usually, the spring 8 provided in the bottom chamber 7b of the cylinder 7 is used.
Thus, the clutch mechanism 6 is maintained at the disconnection position, and the hydraulic motor 3 is disconnected from the variable displacement pump 1 side. When a predetermined pressure is guided to the rod side chamber 7a of the cylinder 7, the clutch mechanism 6 is switched to the linked state by the thrust of the cylinder 7, and the hydraulic motor 3 is linked to the variable displacement pump 1 side. The cylinder 7 and the spring 8
This constitutes the clutch switching means in the present invention.

The forward traveling line 2 and the reverse traveling line 4 communicate with each other via a communication line 9.
The communication line 9 is provided with a communication valve 10. The communication valve 10 is in a normal position maintained by the spring 11, and is in a shut-off position for shutting off the communication line 12, as shown in FIG. Then, when a predetermined pilot pressure is introduced into the pilot chamber 12, the position is switched to a communication position for communicating with the communication line 12.

Here, a control pump 13 is connected to the variable displacement pump 1. Therefore, the control pump 13 rotates together with the variable displacement pump 1 by the driving force of the engine E. Then, the suction port 13a of the control pump 13 is connected to the tank T,
The discharge port 13b is connected to the switching valve 14 described below.
Connected to.

The switching valve 14 connected to the control pump 13 is linked to the swash plate of the variable displacement pump 1.
In its normal state, the switching valve 14 is at the low-speed switching position 141 as shown in FIG. At the low speed switching position 141, the discharge port 13b of the control pump 13 is shut off, and the pilot line 15 connected to the rod side chamber 7a of the cylinder 7 and the pilot chamber 12 of the communication valve 10 communicates with the tank T. . The relief valve 1 is provided on the discharge port 13b side of the control pump 13.
6 is connected so that the discharge pressure does not exceed a predetermined pressure.

When the swash plate of the variable displacement pump 1 is inclined at a set angle in the forward traveling range of the vehicle, the switching valve 14 is switched to the high-speed switching position 14h in conjunction with the swash plate. I have. At this high-speed switching position 14h,
The discharge port 13b of the control pump 13 communicates with the pilot line 15. In addition, as this set angle, an angle near the maximum angle in the forward traveling range of the vehicle is set. In other words, the switching valve 14 is switched to the high-speed switching position 14h when the discharge amount of the variable displacement pump 1 becomes close to the maximum amount and the vehicle moves forward at a high vehicle speed.

Next, the operation of the hydrostatic transmission device 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 displacement pump 1. Hereinafter, a case where the swash plate of the variable displacement pump 1 is inclined in the forward traveling range of the vehicle will be described.

First, the operation when the swash plate of the variable displacement pump 1 is tilted in the range from the minimum angle to the set angle will be described. When the swash plate of the variable displacement pump 1 is tilted in the range from the minimum angle to the set angle, the switching valve 14 keeps the normal state, and as shown in FIG.
4l. At the low-speed switching position 141, the discharge port 13b of the control pump 13 is shut off and the pilot line 15 communicates with the tank T as described above.

Accordingly, the rod side chamber 7a of the cylinder 7 and the pilot chamber 12 of the communication valve 10 are maintained at the tank pressure. When the rod-side chamber 7a of the cylinder 7 is maintained at the tank pressure, the clutch mechanism 6 is in the disconnected state, and when the pilot chamber 12 is maintained at the tank pressure, the communication valve 10 is at the closed position. Since the relief valve 16 is connected to the discharge port 13b side of the control pump 13, the discharge pressure of the control pump 13 is maintained at a predetermined pressure, so that a large load is not applied to the engine E.

As described above, when the swash plate of the variable displacement pump 1 is tilted in the range from the minimum angle to the set angle,
That is, when the vehicle is traveling at a low vehicle speed, the clutch mechanism 6 is in the disconnected state, and the communication valve 10 is in the disconnected position. Therefore, it functions as a normal hydrostatic transmission device, and continuously variable speed can be achieved by continuously controlling the rotation speed of the hydraulic motor 3.

Next, the operation when the swash plate of the variable displacement pump 1 is inclined beyond the set angle will be described. When the swash plate of the variable displacement pump 1 is tilted at a set angle, the switching valve 14 is switched to the high-speed switching position 14h in association with the swash plate. At the high-speed switching position 14h, the discharge port 13b of the control pump 13 is connected to the pilot line 15 as described above.

Therefore, the rod-side chamber 7a of the cylinder 7 and the pilot chamber 12 of the communication valve 10 are controlled by a relief pump 14 at a predetermined pressure.
Discharge pressure is introduced. When a predetermined pressure is guided to the rod side chamber 7a of the cylinder 7, the clutch mechanism 6 is switched to the linked state. When a predetermined pressure is guided to the pilot chamber 12, the communication valve 10 is switched to the communication position. .

As described above, when the swash plate of the variable displacement pump 1 is inclined beyond the set angle, that is, when the vehicle is running at a high vehicle speed, the clutch mechanism 6 is switched to the linked state. Therefore, the driving force of the engine E is directly transmitted to the hydraulic motor 3 via the shaft 5, and the driving force of the engine E can be transmitted to the output side most efficiently. Also, since the communication valve 10 is switched to the communication position,
The two traveling lines 2 and 4 communicate with each other via the communication line 12. Accordingly, the two traveling lines 2 and 4 have the same pressure, and the hydraulic motor 3 is not rotated by the discharge oil of the variable displacement pump 1, and there is no possibility that the transmission efficiency is impaired there.

When the vehicle is traveling in reverse, 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.
Also in the above embodiment, when the swash plate of the variable displacement pump 1 is tilted in the reverse traveling range of the vehicle, the switching valve 14 keeps the normal state regardless of the tilt angle, and as shown in FIG. 14l. Therefore, the vehicle always functions as a hydrostatic transmission device when traveling backward.

[0022]

According to the present invention, when the swash plate of the variable displacement pump is tilted in the range from the minimum angle to the set angle in the forward traveling range of the vehicle, that is, at low vehicle speed, the clutch mechanism is in the disengaged state. And the communication valve is in the shut-off position. Therefore, it functions as a normal hydrostatic transmission device, and continuously controls the rotation speed of the fluid pressure motor, thereby enabling stepless speed change. On the other hand, when the swash plate of the variable displacement pump is tilted beyond the set angle in the forward traveling range of the vehicle, that is, during high vehicle speed traveling, the clutch mechanism is switched to the linked state, so the driving force of the power source is reduced. It can be transmitted directly to the fluid pressure motor side. Further, since the communication valve is switched to the communication position, the two traveling lines have the same pressure, and the fluid pressure motor does not rotate by the discharge fluid of the variable displacement pump, so that there is no possibility that the transmission efficiency is impaired there.

[Brief description of the drawings]

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

[Explanation of symbols]

 E engine 1 variable displacement pump 1a, 1b port 2 forward travel line 3 hydraulic motor 3a, 3b port 4 reverse travel line 6 clutch mechanism 7 cylinder 8 spring 9 communication line 10 communication valve 12 pilot chamber 13 control pump 13a suction port 13b discharge Port 14 Switching valve 15 Pilot line

Claims (1)

[Claims] 1. A variable displacement pump which is linked to a power source rotating in one direction and changes a discharge amount and a discharge direction in accordance with a tilt of a swash plate, a fluid pressure motor permitting flow in both directions, and a variable displacement pump. Hydrostatic having a forward traveling line connecting one port of a hydraulic pump to one port of a hydraulic motor, and a reverse traveling line connecting the other port of the variable displacement pump to the other port of the hydraulic motor In a transmission device, a fluid pressure motor is linked to a power source side, or a clutch mechanism that disconnects the linkage, and usually the clutch mechanism is kept in a disconnected state,
A clutch switching means for switching the clutch mechanism to the linked state when a predetermined pressure is introduced, a control pump rotating together with the variable displacement pump, a communication line communicating the forward traveling line and the reverse traveling line, and a communication line. And at the shut-off position that normally cuts off the communication line,
A communication valve that switches to a communication position that communicates with the communication line when a predetermined pressure is guided to the pilot chamber, and a control pump that is used when the swash plate of the variable displacement pump is tilted beyond a set angle in the forward traveling range of the vehicle. And a switching valve for communicating a predetermined pressure to the clutch switching means and the pilot chamber of the communication valve by communicating with the clutch switching means and the pilot chamber of the communication valve.