JP4966250B2 - Hydraulic control device for work vehicle - Google Patents

Description

  The present invention includes a hydrostatic continuously variable transmission for driving a traveling device, a drive system for working power having a PTO clutch and supplying charge oil to the hydrostatic continuously variable transmission. The present invention relates to an improvement of a hydraulic control device for a work vehicle including a charge pump.

As a hydraulic control device for this type of work vehicle, one having the following structure is conventionally known.
[1] Discharge oil from a hydraulic pump for supplying charge pressure to a hydrostatic continuously variable transmission, supply pressure in a plurality of circuits using a regulator valve, circuit pressure suitable for a power steering system, and work A circuit pressure suitable for control of the clutch and servo cylinder is adjusted and supplied (see Patent Document 1).

JP 2002-284024 A (paragraph number 0028, FIG. 12)

In the conventional structure shown in the above [1], the supply pressure in a plurality of circuits can be appropriately set using a regulator valve. For example, a plurality of hydraulic pumps are used for each circuit from the pump. Compared to a structure in which the discharge pressure is set, it is useful in that the structure can be simplified and reduced in size.
However, the structure in which the supply pressure in a plurality of circuits is set using the regulator valve as described above has the following problems.
That is, the regulator valve itself is relatively expensive and it is difficult to sufficiently reduce the cost. Also, since the supply pressure set by the regulator valve is set to a predetermined value for each circuit, the original pressure before branching is always required to be equal to or greater than the sum of the circuit pressures after branching. Will be. Therefore, if the equipment used in each circuit is used only intermittently, the average amount of pressure oil used and the pressure used are relatively small. Since the amount of pressure oil used and the working pressure are required, a pump with a relatively large capacity has been required.

  An object of the present invention is to provide a plurality of circuits branched from a single pump, and to secure a required pressure for a circuit including a PTO clutch while omitting a regulator valve for setting a circuit pressure. It is to obtain a hydraulic control device for a work vehicle that can control and supply pressure oil to a branch circuit including other devices.

[Solution 1]
The technical means of the present invention taken in order to solve the above-described problems includes a hydrostatic continuously variable transmission for driving a traveling device and a PTO clutch in a drive system for working power. A hydraulic control device for a work vehicle including a charge pump for supplying charge oil to the hydrostatic continuously variable transmission,
The discharge oil from the charge pump is supplied in parallel to the charge oil supply circuit of the hydrostatic continuously variable transmission and the PTO clutch control circuit for controlling the operation of the PTO clutch, and is more pressurized than the charge oil supply circuit. The PTO clutch control circuit is configured to be connected to the lower side of the oil supply direction,
In addition to the PTO clutch control circuit, other than for supplying pressure oil to other devices that are intermittently used, in a location on the lower side in the pressure oil supply direction than the branch location to the charge oil supply circuit Branch connection of oil passage for device output
Pressure compensation for throttle operation to reduce the amount of pressure oil supplied to the other device output oil passage when the pressure on the PTO clutch control circuit side drops below the set value at the branch point to the other device output oil passage A valve is provided.

[Action and effect]
As described above, in the hydraulic control device for a working vehicle of the present invention according to the solution 1, the lower side portion in the pressure oil supply direction than the branch point to the charge oil supply circuit, separately from the PTO clutch control circuit, The other device output oil passage for supplying pressure oil to other devices that are intermittently used is branched and connected, and the above-mentioned pressure compensation valve is provided at the branch point to the other device output oil passage. Therefore, it is possible to secure the required pressure to the circuit including the PTO clutch and supply the pressure oil to the branch circuit including the other device.
In other words, when the pressure compensation valve reduces the pressure on the PTO clutch control circuit side and reduces the amount of pressure oil supplied to the oil passage for other device output, the required pressure on the PTO clutch control circuit side is secured. Can be maintained.
The pressure oil supply amount to the other device output oil passage is reduced, but the other device used in the other device output oil passage is originally only used intermittently. If it is not used at the time when is reduced, there is no effect. Moreover, even if it is used, if the required pressure and the required amount do not have to be so large, the influence is still small, and the required pressure on the PTO clutch control circuit side can be secured rather than the malfunction caused by it. The advantage is great.

In addition, as a means for enabling the pressure oil supply to the oil passage for other device output while maintaining the required pressure on the PTO clutch control circuit side, for example, a branch valve is provided at the branch point, It is also conceivable that the PTO clutch control circuit side is the steady flow side and the other device output oil passage side is the surplus flow side. However, such a configuration using a diversion valve cannot cope with a case where the pressure on the secondary side decreases due to pressure fluctuation on the primary side. Compared to this, in the present invention, even if the pressure on the PTO clutch control circuit side is reduced due to the pressure drop on the primary side, the pressure oil supply amount to the oil passage for other device output is automatically reduced, Since the decrease is increased on the PTO clutch control circuit side, there is an advantage that the required pressure on the PTO clutch control circuit side can be easily secured.
Furthermore, since a regulator valve for setting a required pressure for each circuit is not required, it is useful in terms of cost reduction.

[Overall configuration of work vehicle]
FIG. 1 shows an entire side surface of a tractor that is an example of a work vehicle. This tractor is provided with front wheels 3 on the left and right of a front frame 2 that supports the vibration isolation of the engine 1, and with rear wheels 5 on the left and right of a transmission case 4 that also serves as a frame connected to the engine 1. A boarding operation unit 8 including a steering wheel 6 and a driver seat 7 is formed above and formed.
The transmission case 4 includes a first casing portion 4A that houses the main clutch 9 and the like, a second casing portion 4B that houses the hydrostatic continuously variable transmission 10 and the like, a third casing portion 4C that houses the PTO clutch 14 and the like, and The fourth casing portion 4D that houses the gear-type transmission 11 and the like is connected.

As shown in FIG. 2, the power extracted from the engine 1 is transmitted to a hydrostatic continuously variable transmission (an example of a continuously variable transmission) 10 provided as a main transmission via a dry main clutch 9 and the like. Is done.
Of the power extracted from the hydrostatic continuously variable transmission 10, the driving power is transmitted via a gear-type transmission 11 provided as an auxiliary transmission, the front wheel differential 12, or the rear wheel differential 13. Are transmitted to the left and right front wheels 3 and the left and right rear wheels 5. The gear-type transmission 11 is configured to be able to change gears in three stages of high, medium and low.
Of the power extracted from the hydrostatic continuously variable transmission 10, working power is transmitted to the power take-off shaft 15 via the hydraulic PTO clutch 14 and the like.

[Configuration of hydraulic control unit]
As shown in FIG. 3, the hydrostatic continuously variable transmission 10 includes an axial plunger type variable displacement pump 16, a constant displacement motor 17, and the like housed in the second casing portion 4 </ b> B. The speed change power is output as work power, and the speed change power from the constant capacity motor 17 is output as travel power.
The variable displacement pump 16 and the constant displacement motor 17 are connected via a first oil passage 18 and a second oil passage 19, and are driven by engine power together with the variable displacement pump 16 to a closed circuit 20 formed by the connection. Charge oil from the charge pump 21 is supplied through the charge oil passage 22 and the check valve 23.

As shown in FIGS. 1 and 3, the tractor includes a swash plate [transmission operation unit] of the variable displacement pump 16 based on an operation of a transmission pedal (an example of a transmission operation tool) 24 provided in the boarding operation unit 8. Example (hereinafter referred to as “pump swash plate”)] A servo control mechanism 25 that performs a speed change operation by changing the swash plate angle of 16A is provided.
The shift pedal 24 is configured as a neutral return type that automatically returns to a neutral position (zero speed position) by urging by a spring (not shown).

  As shown in FIG. 3, the servo control mechanism 25 controls the hydraulic cylinder 16 servo cylinder (an example of the operating means) 26 for continuously changing the speed of the pump swash plate 16 </ b> A, and the flow of hydraulic oil to the servo cylinder 26. The servo valve 27 is configured to operate in conjunction with the speed change pedal 24. Accordingly, by operating the shift pedal 24, the servo valve 27 supplies hydraulic oil to the forward shift oil chamber 34 of the servo cylinder 26, and the reverse shift oil chamber 35 of the servo cylinder 26 operates. Is switched to the state of supplying

The servo cylinder 26, together with a forward return spring (an example of an urging means) 32 that urges the pump swash plate 16A to return to a neutral position (zero speed position) 32 and a backward return spring (an example of an urging means) 33 The second casing part 4B is internally provided.
Then, the hydraulic oil from the servo valve 27 is supplied to the forward shift oil chamber 34, whereby the pump swash plate 16A is shifted in the forward acceleration direction against the urging force of the return spring 32, and the forward shift is performed. The hydraulic oil is discharged from the speed change oil chamber 34 to allow the speed change operation of the pump swash plate 16 </ b> A in the forward deceleration direction by the biasing of the return spring 32.
Further, when hydraulic oil is supplied to the oil chamber 35 for reverse speed change, the pump swash plate 16A is shifted in the reverse speed increasing direction against the urging force of the return spring 33, and the oil chamber for reverse speed change. As the hydraulic oil is discharged from 35, the shift operation in the reverse deceleration direction of the pump swash plate 16 </ b> A by the biasing of the return spring 33 is permitted.

The pressure oil supply path 30 of the charge pump 21 for supplying charge oil to the closed circuit 20 of the hydrostatic continuously variable transmission 10 is connected to the charge oil path 22 and a PTO clutch control circuit 40 in parallel. Has been.
The PTO clutch control circuit 40 is equipped with a clutch operation cylinder 41 for turning on and off the PTO clutch 14 and a clutch operation valve 45 for supplying and discharging pressure oil to and from the clutch operation cylinder 41.

The clutch operating valve 45 can be switched between two positions in conjunction with the operation of a clutch operating pedal (not shown). When the clutch operating pedal is not depressed, the clutch operating cylinder 41 is shown in FIG. When the spring is biased to the supply position for supplying pressure oil to the side and the clutch operation pedal is depressed, the clutch operation cylinder 41 is moved from the state shown in the figure to the left in the figure, and the pressure operation chamber 42 of the clutch operation cylinder 41 is moved into the pressure receiving chamber 42. Is switched to a discharge position for discharging the pressure oil to the tank side.
When the pressure oil in the pressure receiving chamber 42 is discharged, the clutch operating cylinder 41 is configured to be operated to the clutch disengagement side by the biasing action of the return spring 44 attached to the opposite piston rod chamber 43. It is.

[Pressure compensation valve]
In addition to the charge oil passage 22 and the PTO clutch control circuit 40, the servo control mechanism 25 as the other device output circuit 50 is provided in the pressure oil supply passage 30 to which the discharge oil from the charge pump 21 is supplied. Is connected to the pressure oil supply passage.
The other device output circuit 50 is connected to the pressure oil supply path 30 of the charge pump 21 at a position on the lower side of the pressure oil supply direction than the branch to the charge oil path 22 and the PTO clutch control circuit 40. It connects via the pressure compensation valve 51 so that it may branch.

The pressure compensation valve 51 is configured such that the circuit pressure on the PTO clutch control circuit 40 side is input as the secondary pressure, and the circuit pressure on the PTO clutch control circuit 40 side is equal to or higher than a predetermined pressure. In some cases, as shown in FIG. 3, both the PTO clutch control circuit 40 and the other device output circuit 50 are in the both supply position a where the discharge oil from the charge pump 21 is supplied with its circuit pressure unchanged.
When the circuit pressure on the PTO clutch control circuit 40 side does not reach a predetermined pressure, the pressure setting spring 57 provided in the pressure compensation valve 51 overcomes the input circuit pressure, and the state shown in FIG. The pressure compensation valve 51 is pushed back to the right in the figure to switch to the PTO system priority position b.

  In this PTO system priority position b, the discharge oil from the charge pump 21 is supplied to the PTO clutch control circuit 40 side while maintaining its circuit pressure, but the orifice 59 for throttle is supplied to the other device output circuit 50 side. Therefore, the amount of pressure oil supplied to the other device output circuit 50 side is reduced. As a result, the amount of pressure oil supplied to the PTO clutch control circuit 40 side increases, so that a decrease in circuit pressure in the PTO clutch control circuit 40 can be avoided.

The pressure compensation valve 51 is configured as shown in FIGS. 4 (a) and 4 (b).
The valve case 52 of the pressure compensation valve 51 shown in FIG. 4 includes a pump-side port 53 whose primary side is the pressure oil supply passage 30 on the charge pump 21 side, and a PTO-side port whose secondary side is the PTO clutch control circuit 40. 54 and a servo-side port 55 connected to the other device output circuit 50, and a spool 56 mounted in the valve case 52 has a circuit pressure acting on each port and a built-in pressure setting spring. The pressure oil supply mode to the servo side port 55 is switched in accordance with the balance with 57.

  That is, FIG. 4A shows a state where the circuit pressure of the pump side port 53 and the PTO side port 54 overcomes the pushing force of the pressure setting spring 57 in the valve case 52 and pushes down the spool 56. This state corresponds to the both-side supply position a, and the pressure oil supplied from the pressure oil supply path 30 on the charge pump 21 side is connected to the pump side port 53 and directly connected to the PTO side port 54. Is supplied to the PTO clutch control circuit 40 with the same circuit pressure, and is also formed in the internal passage 56a formed in the spool 56 and the valve case 52 for the other device output circuit 50. The first circuit passage 58a is supplied with the same circuit pressure.

FIG. 4B shows a state in which the circuit pressure at the pump side port 53 and the PTO side port 54 has decreased and becomes lower than the pushing force of the pressure setting spring 57 in the valve case 52. This state corresponds to the PTO system priority position b, and the pushed-up spool 56 closes the first passage 58a of the valve case 52, and the internal passage 56a of the spool 56 serves as the second communication passage 58b of the valve case 52. It is open to.
In the second passage 58b, since the orifice 59 is provided in the middle of the flow path, the amount of pressure oil supplied to the other device output circuit 50 supplied through the orifice 59 is reduced. At this time, there is no throttling action in the passage from the pump side port 53 directly connected to the PTO side port 54, and conversely, the pressure oil supply amount to the other device output circuit 50 is reduced, The amount of pressure oil supplied to the PTO clutch control circuit 40 increases, and the supply pressure is increased.

FIG. 5 shows the engine speed (or pump speed) and the circuit pressure, with the horizontal axis representing the charge pump speed synchronized with the engine speed and the vertical axis representing the discharge pressure of the charge pump 21. It is the graph which showed the correlation.
In the figure, a line segment indicated by a two-dot chain line indicates a correlation when the pressure compensation valve of the present invention is not provided, and a line segment indicated by a solid line in the figure indicates a case where the pressure compensation valve of the present invention is provided. Show. As can be seen from this graph, the pressure compensation valve 51 according to the present invention is switched and operated by the pressure setting spring 57 so that the pressure is about 1.5 MPa and the rotation speed is about 1000 rpm. A range has been set.

[Other Embodiment 1]
In the above-described best embodiment, the other device output circuit 50 has a structure including the servo control mechanism 25. However, the present invention is not limited to this. For example, the shift cylinder for operating the auxiliary transmission in the gear transmission mechanism is operated. Various mechanisms can be employed such as a mechanism that operates a shift cylinder that performs a shift operation in a hydraulic mechanical transmission mechanism.

[Second embodiment]
The work vehicle may be a rice transplanter, a combiner, a mower, a wheel loader, or the like.

Overall side view of tractor Schematic showing the transmission structure of the tractor Hydraulic circuit diagram Sectional view showing pressure compensation valve Graph showing the correlation between circuit pressure and pump input speed

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hydrostatic continuously variable transmission 14 PTO clutch 21 Charge pump 22 Charge oil supply circuit 30 Pressure oil supply circuit 40 PTO clutch control circuit 50 Other apparatus output circuit 51 Pressure compensation valve

Claims (1)

In addition to a hydrostatic continuously variable transmission for driving the traveling device, a PTO clutch is provided in the drive system for working power, and a charge pump is provided for supplying charge oil to the hydrostatic continuously variable transmission. Hydraulic control device for a working vehicle,
The discharge oil from the charge pump is supplied in parallel to the charge oil supply circuit of the hydrostatic continuously variable transmission and the PTO clutch control circuit for controlling the operation of the PTO clutch, and is more pressurized than the charge oil supply circuit. The PTO clutch control circuit is configured to be connected to the lower side of the oil supply direction,
In addition to the PTO clutch control circuit, other than for supplying pressure oil to other devices that are intermittently used, in a location on the lower side in the pressure oil supply direction than the branch location to the charge oil supply circuit Branch connection of oil passage for device output
Pressure compensation for throttle operation to reduce the amount of pressure oil supplied to the other device output oil passage when the pressure on the PTO clutch control circuit side drops below the set value at the branch point to the other device output oil passage A hydraulic control device for a work vehicle, comprising a valve.

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