JP2001235031A - Hydrostatic continuously variable transmission for working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an HSGT(hydrostatic continuously variable transmission) at low cost which is capable of increasing outputs whenever necessary according to the contents of operations, with the capacity of the HST being determined in accordance with output requests frequency used under normal conditions. SOLUTION: The hydrostatic continuously variable transmission (HST) 20 includes a variable hydraulic pump 51 and a hydraulic motor 52 driven by the hydraulic pump 51. A port pressure applied to the tilt angle changing port 57 of the hydraulic motor 52 can be varied in two steps by movement of a directional control valve 58 which is moved by a solenoid selector valve 43. The solenoid selector valve 43 and the directional control valve 58 are stably operated under constant pressure by applying the delivery fluid of a subsidiary pump through a pressure reducing valve 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrostatic continuously variable transmission for a working vehicle, and more particularly to a hydrostatic continuously variable transmission for a working vehicle such as a tractor or a rice transplanter.

[0002]

2. Description of the Related Art In a relatively small work vehicle, there is known one in which the engine power is shifted by a hydrostatic continuously variable transmission (HST). The HST is configured by combining a variable hydraulic pump driven by engine power and a hydraulic motor driven by the hydraulic pump, and by changing the tilt angle of the hydraulic pump by rotation of the trunnion shaft, The rotation of the hydraulic motor is steplessly shifted and output.

[0003] However, output demands on the HST are different when traveling at high speed on a road or the like and when traveling with a load applied with a work implement. When an HST having a large capacity is mounted in accordance with the maximum output demand, the driving horsepower becomes large, and wasteful horsepower is consumed even when the output demand is small, which is inefficient and fuel is consumed. Is uneconomical. on the other hand,
When an HST having a small capacity is mounted and the output demand is large, the output torque can be increased by the transmission, but the operability is deteriorated because the number of gears of the auxiliary transmission increases.

[0004] Here, an actuator for changing the tilt angle of the internal swash plate is provided in the hydraulic motor of the HST, and the hydraulic oil from the charge circuit of the HST is supplied to the actuator by a switching valve to thereby output the output of the HST. Although it is possible to arbitrarily change it, the operating pressure for driving the actuator may exceed the HST charge relief pressure, and in such a case, the charge filter or the oil cooler may be damaged.

[0005] Therefore, there is a technical problem to be solved in order to obtain an HST in which the capacity of the HST is determined in accordance with the output requirement which is frequently used and the output can be surely increased at any time according to the work contents, at a low cost. Therefore, the present invention aims to solve this problem.

[0006]

SUMMARY OF THE INVENTION The present invention has been proposed to achieve the above object, and is driven by the rotational power of an engine, and changes the discharge amount in response to the depressing operation of a shift pedal. In a work vehicle equipped with a hydrostatic continuously variable transmission including a variable hydraulic pump and a hydraulic motor driven by the hydraulic pump, the tilt angle of the internal swash plate is stepped to the hydraulic motor. The present invention also provides a hydrostatic continuously variable transmission for a working vehicle configured to provide an actuator for changing the hydraulic pressure to a hydraulic oil source of the actuator via a pressure reducing valve provided in a discharge oil passage of a pump.

[0007]

An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a tractor 10 as an example of a work vehicle. An engine 11 is mounted on a front part of the fuselage, covered with a hood 12, a transmission case 13 is attached to a rear part of the fuselage, and a cabin 14 is
And a driver's seat 15 is provided in the cabin 14. A clutch housing 16 is mounted on a rear portion of the engine 11, and a main clutch 17 is provided inside the clutch housing 16.

The main clutch 17 and the transmission case 1
3 is provided with a hydrostatic stepless transmission (HST) 20. The rotational power of the engine 11 is input to the HST 20 via the main clutch 17, and the speed is continuously changed by the HST 20. It is configured to be transmitted to the transmission case 13 later. In the transmission case 13, the power shifted by the HST 20 is branched into the power of the traveling system and the power of the PTO system, and the power of the traveling system is shifted by the gear type transmission 21, and the rear differential device 22 is operated. Then, the rear wheel 23 is driven, and the front wheel 26 is driven from the front wheel transmission shaft 24 via the front differential device 25. On the other hand, the power of the PTO system is output from a PTO output shaft 27 protruding from the rear surface of the transmission case 13.

As shown in FIGS. 2 to 5, the main pump 30 and the sub-pump 31 of the hydraulic circuit
Hydraulic oil discharged from the main pump 30 is supplied to the working machine lifting / lowering main cylinder 33 via the electromagnetic control valve 32. On the other hand, the sub pump 31
The hydraulic oil discharged from the power steering steering unit 35 passes through a pressure reducing valve 34 provided on the front surface of the engine 11.
Supplied to The hydraulic oil from the sub-pump 31 is branched from the pressure reducing valve 34 to the pipe L ₁ , sent to the 4WD clutch 37 via the electromagnetic control valve 36, and supplied to the forward / reverse switching clutch 39 via the electromagnetic control valve 38. .

The power steering steering unit 35
Hydraulic fluid used in the oil cooler 40 from the pipe L ₃
And the charge filter 41, the pipe L ₂ , and the HS
It is introduced to the charge port B of T20. The charge filter 41 is provided with a charge relief valve 42. An electromagnetic switching valve 43 is connected to the control port PC of the HST 20. When the electromagnetic switching valve 43 is in the normal position (a), the control port PC communicates with the tank 45, and the electromagnetic switching valve 43 is in the offset position (b). Then the pressure reducing valve 3
The hydraulic oil branched from 4 is introduced into the control port PC. The excess hydraulic oil in the HST 20 returns to the tank 45 from the tank port T.

The charge filter 41 and the electromagnetic switching valve 4
Numeral 3 is provided on the left side in the traveling direction of the transmission case 13 (hereinafter simply referred to as left side), and the fuel sub-tank 46 and the charge filter 41 are attached to the floor support bracket 47 on the left side. Accordingly, the hydraulic piping is concentrated on one side of the transmission case 13 and the number of connecting portions of the piping is reduced, so that the assembling work is simplified and the maintainability can be improved.

The HST 20 is a clutch housing 16
The HST 20 is mounted on a rear wall of the transmission case 13 and includes a variable hydraulic pump 51 driven by the rotational power of the engine 11 and a hydraulic motor 52 driven by the hydraulic pump 51. Is housed in a case 53 fixed integrally with the case. The rotational power of the engine 11 is turned on and off by the main clutch 17 and is input to the hydraulic pump shaft 54 of the HST 20 via the main clutch 17. The trunnion shaft 55 protruding from the side of the hydraulic pump 51 rotates when the HST pedal 56 is depressed forward or backward, and the discharge amount of the hydraulic pump 51 varies steplessly according to the depression angle of the HST pedal 56. Is changed to

Here, the port pressure applied to the tilt angle switching port 57 for changing the tilt angle of the internal swash plate of the hydraulic motor 52 is switched in two stages by a directional control valve 58. Usually, the directional control valve 58 Is in the normal position (C) and the tilt angle switching port 57 is in communication with the tank 45, so that the port pressure is low. Therefore, the hydraulic motor 52
Becomes small, and the motor shaft 60 rotates with low torque in accordance with the discharge amount of the hydraulic pump 51. That is, the state becomes suitable for high-speed running of the aircraft. An angle sensor 61 is attached to the trunnion shaft 55, and the angle sensor 61
The rotation angle of the trunnion shaft 55 is detected by the
The neutral position of 20 is determined. Also, a rotation sensor 62 is provided on the motor shaft 60, and the rotation sensor 62
The output speed of T20 is detected to calculate the vehicle speed.

If the electromagnetic switching valve 43 is switched to the offset position (b) by a command from a controller (not shown), the oil discharged from the sub-pump 31 passes through the pressure reducing valve 34 and the direction control valve. Acting on the pilot port 58, the direction control valve 58 switches to the offset position (d). Accordingly, the discharge oil of the hydraulic pump 51 acts on the tilt angle switching port 57 to increase the port pressure, and the tilt angle of the hydraulic motor 52 increases, so that the motor shaft 60 rotates with high torque. That is, the state is suitable for a high-load operation. An actuator for changing the tilt angle of the hydraulic motor 52 in a stepwise manner from a directional control valve 58 for switching the port pressure applied to the tilt angle switching port 57 and an electromagnetic switching valve 43 for switching the pilot pressure of the directional control valve 58 Is configured.

As described above, the drive oil source of the direction control valve 58 for changing the tilt angle of the hydraulic motor 52 stepwise is taken in through the pressure reducing valve 34 provided in the discharge oil passage of the sub-pump 31. Therefore, the electromagnetic switching valve 43 and the direction control valve 58 operate at a constant pressure, and the switching operation is always performed with a stable operation, as compared with the configuration using the operating oil from the charging circuit of the HST 20. Also, HS
Since the charge circuit of T20 does not have an excessively high pressure, there is no need to increase the pressure resistance of the oil cooler 40, the charge filter 41, and the like, and a configuration for changing the tilt angle of the hydraulic motor 52 stepwise can be formed at low cost. .

The present invention can be variously modified without departing from the spirit of the present invention, and it goes without saying that the present invention extends to the modified ones.

[0017]

As described in detail in the above embodiment, the present invention mounts a hydrostatic continuously variable transmission (HST) on a work vehicle and controls the tilt angle of a hydraulic motor of the HST in a stepwise manner. The actuator is operated at a constant pressure, so that the hydraulic oil source of the actuator is taken in through a pressure reducing valve provided in the discharge oil passage of the pump. The switching operation can be performed with certainty.

In this manner, the capacity of the HST can be determined according to the output demand that is frequently used, and the output can be increased at any time according to the work content without wasting the horsepower. This is an invention that has a truly remarkable effect, such as being able to contribute to improvement of reliability by reliable switching operation.

[Brief description of the drawings]

 The figure shows an embodiment of the present invention.

FIG. 1 is a side view of a tractor.

FIG. 2 is a side view of an engine and a transmission case.

FIG. 3 is a front view of an engine and a transmission case.

FIG. 4 is a hydraulic circuit diagram.

FIG. 5 is a hydraulic circuit diagram showing a main part.

[Explanation of symbols]

 Reference Signs List 10 Tractor 11 Engine 20 Hydrostatic stepless transmission (HST) 31 Subpump 34 Pressure reducing valve 43 Electromagnetic switching valve 51 Hydraulic pump 52 Hydraulic motor 56 HST pedal 57 Tilt angle switching port 58 Direction control valve

Claims (1)

[Claims] A variable hydraulic pump that is driven by the rotational power of an engine and that changes a discharge amount in accordance with a depressing operation of a shift pedal; and a hydraulic motor that is driven by the hydraulic pump. In a work vehicle equipped with a hydraulic continuously variable transmission, an actuator for changing the tilt angle of an internal swash plate in a stepwise manner is provided in the hydraulic motor, and a hydraulic oil source of the actuator is connected to a discharge oil passage of a pump. A hydrostatic continuously variable transmission for a work vehicle, characterized in that the work is taken in via a pressure reducing valve provided.