JPH018084Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a hydraulic circuit for a tractor, and is designed to ensure that the horizontal control circuit operates reliably even during the lifting and lowering operations of the working machine, especially during the lifting operation.

A pair of lift rods are attached to the tractor via a three-point link mechanism, and connect a pair of left and right lift arms of a lifting cylinder for raising and lowering the work machine and a pair of left and right lower links of the three-point link mechanism; Either one is composed of a hydraulic cylinder, and this hydraulic cylinder (lift rod cylinder)
There is a technology in which the tractor is expanded and contracted using a solenoid valve that responds to a horizontal sensor, so that the work equipment is always controlled horizontally regardless of the inclination of the tractor. The horizontal control circuit including this lift rod cylinder and solenoid valve is
Normally, a lifting circuit including a lifting cylinder and its control valve is connected to a hydraulic pump via a diversion valve, and one hydraulic pump is used for both lifting and horizontal control, and the frequency of use for horizontal control is Since the flow rate is limited, if the return oil from the horizontal control circuit were returned directly to the tank, the flow rate would always be wasted, so a circuit configuration was adopted in which the return oil path merges into the lifting circuit via a check valve. The oil after merging is used to operate the lifting cylinder. However, with such a circuit configuration, considering the pressure in the circuit when both circuits are in operation, the pressure in the lifting circuit when the work equipment is raised is greater than the pressure in the horizontal control circuit during horizontal control. A problem arises in that the flow of return oil is cut off while the work implement is being raised, causing the horizontal control circuit to become inoperable. Therefore, when horizontal control of the work equipment is performed at the same time as draft control is performed to operate the lifting cylinder by sensing fluctuations in the traction load, the horizontal control operation of the work equipment starts after the work equipment lifts/lowers. This results in a significant loss of the significance of horizontal control.

The purpose of this invention is to solve these conventional problems, and its feature is that the lifting circuit of the work equipment and the horizontal control circuit of the work equipment are connected via a shunt valve. In a tractor hydraulic circuit that is connected to a hydraulic pump and has the return oil path of the horizontal control circuit merge into the lifting circuit via a check valve, the horizontal control circuit is connected upstream of the check valve in the return oil path during horizontal control operation. An on-off valve is provided to open the return oil passage using pilot pressure.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiment. In FIG. 1, reference numeral 1 denotes a tractor, and a single-acting lifting cylinder 2 for raising and lowering a working machine at the rear.
is mounted, and the elevating cylinder 2 has a pair of left and right lift arms 3. Reference numeral 4 denotes a plow, which is an example of a working machine, and is attached to the rear of the tractor 1 via a three-point linkage mechanism 5, and is raised and lowered by a lift cylinder 2 via a pair of left and right lift rods 6 and a lift arm 3. One of the pair of left and right lift rods 6 is composed of a telescopic lift rod cylinder 6a, and by expanding and contracting the lift rod cylinder 6a, the plow 4 can be controlled horizontally regardless of the inclination of the tractor 1. be.

FIG. 2 shows a hydraulic circuit including the lifting cylinder 2 and the lift rod cylinder 6a. In FIG. 2, 7 is an engine, and 8 is a hydraulic pump driven by the engine 7. This hydraulic pump 8 sucks oil in a tank 9 and discharges it to the flow dividing valve 10 side. The diversion valve 10 transfers oil supplied from the hydraulic pump 8 to the inlet oil passage 13 between the lifting circuit 11 and the horizontal control circuit 12.
14, and is configured to preferentially divert the flow to the horizontal control circuit 12 side.
In addition to the lifting cylinder 2, the lifting circuit 11 includes a control valve 15, a check valve 16, a throttle valve 17, and an unloading valve 18 to control the lifting cylinder 2. Spool 1 via control lever, feedback mechanism, etc.
By reciprocating 9 in the axial direction, it operates for position control and draft control. The horizontal control circuit 12 includes a lift rod cylinder 6a, a solenoid valve 20, and a check valve 21, and the solenoid valve 20 has a pair of solenoids 22 and 23 driven by the output of a horizontal sensor on the plow side. By selectively energizing the solenoids 22 and 23, the lift rod cylinder 6a is controlled to expand and contract so that the plow 4 is horizontal. A return oil passage 24 of the horizontal control circuit 12 is connected to the inlet oil passage 13 of the lifting circuit 11 via a check valve 25, and a solenoid valve 20 and a check valve 25 are connected to the return oil passage 24. In between, the return oil path 2
An on-off valve 26 for opening 4 is interposed. The on-off valve 26 is of a pilot type, and its pilot circuit 27 connects to the lift rod cylinder 6a.
An oil passage 28 connects the lift rod cylinder 6a and the solenoid valve 20 so that the opening/closing valve 26 is opened by the pilot pressure of the horizontal control circuit 12 during the expansion and contraction operation of the lift rod cylinder 6a.
29. 30 and 31 are relief valves, and 32 is a safety valve.

Next, the effect will be explained. When the hydraulic pump 8 is driven, oil from the tank 9 is sucked in and discharged to the diversion valve 10 side.
It is supplied to 4. When the control valve 15 is in the neutral state, the unload valve 18 opens, and the oil supplied to the lifting circuit 11 side is returned from the inlet oil path 13 to the tank 9 via the unload valve 18, and the control valve 15 to the lifting side, the unload valve 18 closes and the check valve 16 opens, so oil is supplied to the lifting cylinder 2 via the check valve 16, and the lifting cylinder 2 operates to move the plow 4. Lift up.

On the other hand, when the horizontal control is stopped or the plow 4 is horizontal, the solenoid valve 20 is in a neutral state, so the oil supplied to the inlet oil path 14 of the horizontal control circuit 12 is
The oil that flows from the electromagnetic valve 20 to the inlet oil passage 13 of the lifting circuit 11 via the on-off valve 26 of the return oil passage 24 and the check valve 25, and is branched to the horizontal control circuit 12, is used for the lifting circuit 11. It can be used to operate the cylinder 2, preventing wastage of oil.

When the plow 4 tilts and the horizontal sensor detects this, the solenoid valve 20 switches to the upward or downward side,
The plow 4 is moved by the expansion and contraction of the lift rod cylinder 6a.
It moves to return to a horizontal position. Now, if the solenoid 23 is energized and the solenoid valve 20 is switched to the upward side, the oil in the inlet oil passage 14 of the horizontal control circuit 12 passes through the solenoid valve 20, the oil passage 28, and the check valve 21, and then reaches the lift rod. It is supplied to the lower cylinder chamber of the cylinder 6a, and the lift rod cylinder 6
The oil in the upper cylinder chamber of a is connected to the oil passage 29 and the solenoid valve 2.
0 and returns to the return oil path 24, and the lift rod cylinder 6a returns the plow 4 to the horizontal position as a contraction operation. At this time, if the lifting cylinder 2 is not in the ascending operation, the pressure in the inlet oil passage 13 of the lifting circuit 11 is not high pressure, so the return oil enters from the return oil passage 24 via the check valve 25. Side oil passage 1
Join 3. Further, if the lifting cylinder 2 is in the ascending operation due to draft control or the like, the pressure in the inlet oil passage 13 is high, so the check valve 25 does not open, and therefore the return oil does not join the inlet circuit 13. However, at this time, the pressure on the oil passage 28 side of the horizontal control circuit 12 rises above the pilot pressure set by the on-off valve 26, and this on-off valve 26 opens, so the return oil flows from the on-off valve 26 to the tank 9. As it is returned, the lift rod cylinder 6a retracts smoothly and reliably.

The same holds true when the lift rod cylinder 6a is extended.

In the above embodiment, the on-off valve 26 is opened only when the lift cylinder 2 is being raised and the lift rod cylinder 6a is extended or retracted. However, by changing the set value of the pilot pressure of the on-off valve 26, The opening/closing valve 26 may be always opened when the lift rod cylinder 6a is extended or contracted, regardless of the raising operation of the elevating cylinder 2.

The present invention has an on-off valve installed upstream of the check valve in the return oil path, which opens the return oil path using the pilot pressure of the horizontal control circuit during horizontal control operation. Even though the horizontal control circuit is configured to merge into the lifting circuit, it is possible to operate the horizontal control circuit reliably even when the lifting circuit is in operation. Even when the horizontal control of the working machine is performed at the same time, there is no delay in the horizontal control of the working machine, and its practical value is extremely great.

[Brief explanation of the drawing]

The drawings illustrate one embodiment of the present invention, with FIG. 1 being a side view and FIG. 2 being a hydraulic circuit diagram. 1...Tractor, 2...Lifting cylinder, 4...
Plow, 6a... Lift rod cylinder, 8...
Hydraulic pump, 10...Diversion valve, 11...Elevating circuit, 12...Horizontal control circuit, 13, 14...Inlet oil path, 24...Return oil path, 26...Opening/closing valve.

Claims (1)

[Scope of utility model registration request] In the hydraulic circuit of a tractor, the lifting circuit of the working equipment and the horizontal control circuit of the working equipment are connected to a hydraulic pump via a diversion valve, and the return oil path of the horizontal control circuit is joined to the lifting circuit via a check valve. 1. A hydraulic circuit for a tractor, characterized in that an on-off valve is installed upstream of a check valve in a return oil path to open the return oil path using pilot pressure of the horizontal control circuit during horizontal control operation.