JPS62246604A - Hydraulic circuit structure of working vehicle - Google Patents

Abstract

PURPOSE:To obtain normal contracting operation, by providing the No.1 bypass oil passage with a normally-opened pilot valve, which is closed only when the pressure oil is supplied, together with providing the No.2 bypass oil passage with a non-return valve. CONSTITUTION:A piston-rod-side oil chamber 5b is connected to a non-return valve 11 via the No.1 bypass oil passage 14. At the same time, the chamber 5b is connected to the suction side of a pump 8 via the No.2 bypass oil passage. The No.1 bypass oil passage 14 is provided with a pilot valve 17, which is normally open and is closed only when the pressure oil is supplied, while the No.2 bypass oil passage 15 is provided with a non-return valve 18. With this contrivance, the oil in a hydraulic cylinder 5 can completely be discharged when the hydraulic cylinder 5 is operated toward the discharge side. Therefore, normal contracting operation of the hydraulic cylinder can be ensured.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a working device that is attached to a machine body using a single-acting hydraulic cylinder so that it can be raised and lowered freely, and that pressurized oil from a pump is supplied to the hydraulic pressure via a control valve. The present invention relates to a hydraulic circuit structure for a working vehicle in which oil is supplied to a cylinder and a drainage path from the hydraulic cylinder is connected to the suction side of a pump.

[Conventional technology]

The hydraulic circuit structure of work vehicles that use single-acting hydraulic cylinders to raise and lower work equipment is often of the open-loop type, in which transmission oil is supplied to the hydraulic cylinder through a filter, and then drained back into the transmission case. It is used.

In this case, in order to prevent metal powder, abrasion powder, etc. in the transmission case from entering the hydraulic circuit, the smaller the fill gap, the earlier the fill will occur. There is a problem that the pump suction efficiency decreases.
Therefore, as mentioned above, it was devised to adopt a closed-loop hydraulic circuit in which the oil discharge path from the hydraulic cylinder is connected to the suction side of the pump.

In this closed-loop hydraulic circuit, a charge pump is generally provided on the suction side of the pump to compensate for the lack of oil in the circuit due to oil leakage or the like.

[Problem that the invention seeks to solve]

According to this configuration, since the closed-loop hydraulic circuit Kid charge pump pressure is always generated as the reference pressure, when the control valve is operated to the oil drain side and the hydraulic cylinder is contracted by the work equipment's own gravity, the charge pump pressure is Acts as resistance.

For this reason, when the work equipment is particularly light, when lowering only the lifting device such as a 7-torer 8, etc., the oil is not sufficiently drained from the hydraulic cylinder, resulting in an extremely low descending speed or the inability to descend. .

The purpose of the present invention is to provide a structure in which when the hydraulic cylinder is operated to the oil draining side in the closed-loop hydraulic circuit structure as described above, the oil is sufficiently drained from the hydraulic cylinder and the cylinder is normally contracted. It is easy to configure.

[Means for solving problems]

The present invention is characterized in that, in the above-mentioned hydraulic circuit structure for a work vehicle, a first bypass oil passage that communicates between a hydraulic cylinder and a control valve and an oil supply on the piston rod side of the hydraulic cylinder, and the oil chamber are provided. and the second pump suction side.
A bypass oil passage is provided, and a normally open pilot valve that is closed by pilot pressure when the hydraulic cylinder is operated to the pressure oil supply side is provided in the first bypass oil passage, 1'r.
The second bypass oil passage is provided in the check valve 1 which allows the oil chamber to communicate with the pump suction side, and its functions and effects are as follows.

[For production]

For example, when the operation is performed on the pressure oil supply side, the first bypass oil passage is closed by the pilot valve due to the pilot pressure of the pressure oil, pressure oil is supplied to the oil chamber on the bottom side of the hydraulic cylinder, and the hydraulic cylinder is operated to extend. When operating from this state to the oil drain side, the pilot pressure decreases and the pilot valve opens, so that part of the oil drained from the oil chamber on the bottom side of the cylinder flows into the first oil chamber.
The oil is also sent through the bypass oil passage to the oil chamber on the piston rod side of the hydraulic cylinder, thereby promoting the contraction operation of the hydraulic cylinder. In this state, when the operation is made to the pressure oil supply side, the pilot valve closes again and pressure oil is supplied to the oil chamber at the bottom of the cylinder, and the oil in the oil chamber on the piston rod side is discharged through the second bypass oil passage. I am going.

〔Effect of the invention〕

As explained above, a hydraulic circuit structure has been obtained that allows the single-acting hydraulic cylinder operated by a closed-loop hydraulic circuit for lifting and lowering work equipment to be extended and contracted without any problems, thereby improving the operability and safety of lifting and lowering work equipment. has improved. Additionally, a structure in which the opening and closing operations of the first and second bypass oil passages are performed by an on-off valve linked to a control valve is also considered, but in this case, the hydraulic circuit would be complicated due to restrictions on the arrangement of the oil passage and the on-off valve. By using a pilot valve and check valve, which have a simpler structure and lower cost than such a structure, it is possible to provide the above-mentioned functions while providing flexibility in the arrangement of the oil passage and six valves. The hydraulic circuit has a relatively simple structure, and
This provides an advantageous structure in terms of cost.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings, using an agricultural tractor as an example of a working vehicle.

As shown in Fig. 2, the working device (4) is connected to the rear of the traveling machine via a J-point link mechanism (3) consisting of a pair of left and right lower links (11, (11) and a wooden top link (2)).
) is connected so as to be able to rise and fall freely, and is further oscillated by a single-acting hydraulic cylinder 15) and a lower link Tll,
11) and the rotary tillage device (71? (connected via 71t, hydraulic cylinder) 5).
4) The agricultural tractor is constructed so that it can be fully raised and lowered.

Next, the pre-pressure circuit that supplies hydraulic oil to the hydraulic cylinder (5) will be explained in detail.As shown in Fig. Pressure oil from the pump (8) is supplied to the J position switching type control valve (9).
) is supplied to the oil chamber (5a) on the cylinder bottom side of the hydraulic cylinder (5) via an oil passage 4101 provided with a check valve (Il+ and a variable throttle part (Iφ), and from the control valve (9). A drain oil passage 021 is connected to the suction side of the pump (8), and a charge pump 021 is connected to the suction side of the pump (8).
31 are provided.

The hydraulic cylinder (oil chamber (5b) on the piston rod side in 5+) and the check valve (hydraulic cylinder (5))
5) side, and a second bypass oil passage system that communicates the oil chamber (5b) with the suction side of the pump (8).

The above-mentioned check valve (
11) and the control valve (9), a normally open pilot valve (iη, second bypass oil path 0
5) is provided with a check valve that allows communication from the hydraulic cylinder (5) to the suction side of the pump (8).

Fig. 1 shows a state in which the control valve (91k) is operated in the neutral position -, but for example, a state in which pressure oil is supplied to the oil chamber (5s+) on the bottom side of the cylinder, that is, the rotary tiller 14
) is operated upwards, and if the control valve (3) is operated to the downward side ), the pilot pressure between the check valve (11) and the control valve (9) decreases, and the pilot valve 0η goes down. For the sake of
Part of the drained oil from the oil chamber (5a) on the bottom side of the cylinder
The bypass oil passage 04 is passed through the oil chamber (5b) of the piston rod example.
) to promote the contraction operation of the hydraulic cylinder (5).

The lowering operation of the rotary tiller (4) is performed smoothly.

Next, when the switching valve (ol) is operated to the rising side (5), the pilot pressure between the check valve (11) and the control valve (9) increases, which closes the pilot valve Oη and pumps (8). ) is supplied to the oil chamber (5a) K on the bottom side of the cylinder, and the oil that was in the oil chamber (5b) on the piston rod side is discharged through the second bypass oil path side. It is.

Note that although numbers are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure of the accompanying drawings by these numbers.

[Brief explanation of drawings]

The drawings show an embodiment of the hydraulic circuit structure for a working vehicle according to the present invention, and FIG. 1 is a hydraulic pressure supply circuit diagram, and FIG. 2 is a side view of the rear half of an agricultural tractor to which a rotary tilling device is attached. (4)... Working equipment, (5)... Hydraulic cylinder, (5b)... Oil i on the piston rod side, (81... Pump, (9)・・・・・・
Control valve, Q21... Oil drain path s H...
・First bypass oil path, +161...Second bypass oil path, (17)...Pilot valve, 0 (5)
······non-return valve.

Claims (1)

[Claims] The working device (4) is attached to the machine body by a single-acting hydraulic cylinder (1) so that it can be raised and lowered freely, and the pressure oil from the pump (8) is supplied to the hydraulic cylinder (5) via the control valve (9).
) and a drain path (12) from the hydraulic cylinder (5).
This is a hydraulic circuit structure of a work vehicle in which the hydraulic cylinder (5) and the control valve (9) are connected to the suction side of the pump (8).
) and the oil chamber (5b) on the piston rod side of the hydraulic cylinder (5).
4) and providing a second bypass oil passage (15) connecting the oil chamber (5b) and the suction side of the pump (8),
A normally open pilot valve (17) that closes with pilot pressure when operated to the pressure oil supply side with respect to the hydraulic cylinder (5).
is provided in the first bypass oil passage (14), and a pump (8) is provided from the oil chamber (5b) to the second bypass oil passage (15).
A hydraulic circuit structure of a work vehicle equipped with a check valve (18) that allows communication to the suction side.